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using DbContext in a manually created scope in a singleton service results in ObjectDisposedException

Note: In the hour I spent writing this post and in the process having a second and third look at everything, I found the solution to my problem. I decided to post this anyway, as I did not find the solution online and it might help others.
If you have any comments about my architecture, please do share them! My guts tell me I should not have stumbled across this problem in the first place, but I can't point my finger to a specific detail.
In my .NET 6 application I have a service which needs to access the database, thus use a DbContext. The service is registered as singleton, but the DbContext is not, as it should be. Quite a number of similar questions out there are answered with inject IServiceScopeFactory and create (and dispose) your scope for each operation. example 1, example 2, example from Microsoft.
I try to do exactly that, but it throws ObjectDisposedExceptions, so it obviously does not work in my case. The question is: why?
The service(s) I'm talking about are data access services for the rest of the application, the gateway to the database. They are registered as singletons, because they fire events consumed by background services for certain actions.
I moved the context and scope handling into an abstract class, that looks like this (stripped down):
(I obviously renamed all classes, I'm not working on a cat related application, if something does not add up, I might have forgotten to remane something 😁)
public abstract class RepositoryBase
{
private readonly IServiceScopeFactory serviceScopeFactory;
protected RepositoryBase(IServiceScopeFactory serviceScopeFactory)
{
this.serviceScopeFactory = serviceScopeFactory;
}
protected void ExecuteInContext(Action<IAnimalContext> function)
{
using var scope = serviceScopeFactory.CreateScope();
function(scope.ServiceProvider.GetRequiredService<IAnimalContext>());
}
protected T ExecuteInContext<T>(Func<IAnimalContext, T> function)
{
using var scope = serviceScopeFactory.CreateScope();
return function(scope.ServiceProvider.GetRequiredService<IAnimalContext>());
}
}
This is then used like so:
internal class CatRepository : RepositoryBase, ICatRepository
{
public CatRepository(IServiceScopeFactory serviceScopeFactory) : base(serviceScopeFactory)
{ }
public event Action<Guid>? CatRenamed;
public IEnumerable<Cat> AllCats => ExecuteInContext(context => context.Cats);
public void RenameCat(Guid id, string name) => ExecuteInContext(context => {
var cat = context.Cats.FindOrThrow(id);
cat.Name = name;
context.SaveChanges();
CatRenamed?.Invoke(cat.id);
});
If I'm removing the using statements from the ExecuteInContext functions, it behaves as expected (creating a new scope every time a repository action is called and never disposing the scopes).
Debugging with breakpoints (as well as log messages) in the ExecuteInContext functions indicate that the actions are executed completely before the scope is disposed.
The stack trace of the exception has no functions or classes written by me in it. When calling CatRepository.AllCats it looks something like this:
fail: Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware[1]
An unhandled exception has occurred while executing the request.
System.ObjectDisposedException: Cannot access a disposed context instance. A common cause of this error is disposing a context instance that was resolved from dependency injection and then later trying
to use the same context instance elsewhere in your application. This may occur if you are calling 'Dispose' on the context instance, or wrapping it in a using statement. If you are using dependency injectio
n, you should let the dependency injection container take care of disposing context instances.
Object name: 'LogisticsStateManagementContext'.
at Microsoft.EntityFrameworkCore.DbContext.CheckDisposed()
at Microsoft.EntityFrameworkCore.DbContext.get_ContextServices()
at Microsoft.EntityFrameworkCore.DbContext.get_InternalServiceProvider()
at Microsoft.EntityFrameworkCore.DbContext.get_ChangeTracker()
at Microsoft.EntityFrameworkCore.Query.CompiledQueryCacheKeyGenerator.GenerateCacheKeyCore(Expression query, Boolean async)
at Microsoft.EntityFrameworkCore.Query.RelationalCompiledQueryCacheKeyGenerator.GenerateCacheKeyCore(Expression query, Boolean async)
at Microsoft.EntityFrameworkCore.SqlServer.Query.Internal.SqlServerCompiledQueryCacheKeyGenerator.GenerateCacheKey(Expression query, Boolean async)
at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.Execute[TResult](Expression query)
at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryProvider.Execute[TResult](Expression expression)
at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable`1.GetEnumerator()
at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.IncludableQueryable`2.GetEnumerator()
at System.Linq.Enumerable.SelectEnumerableIterator`2.MoveNext()
at System.Text.Json.Serialization.Converters.IEnumerableDefaultConverter`2.OnWriteResume(Utf8JsonWriter writer, TCollection value, JsonSerializerOptions options, WriteStack& state)
at System.Text.Json.Serialization.JsonCollectionConverter`2.OnTryWrite(Utf8JsonWriter writer, TCollection value, JsonSerializerOptions options, WriteStack& state)
at System.Text.Json.Serialization.JsonConverter`1.TryWrite(Utf8JsonWriter writer, T& value, JsonSerializerOptions options, WriteStack& state)
at System.Text.Json.Serialization.JsonConverter`1.WriteCore(Utf8JsonWriter writer, T& value, JsonSerializerOptions options, WriteStack& state)
at System.Text.Json.Serialization.JsonConverter`1.WriteCoreAsObject(Utf8JsonWriter writer, Object value, JsonSerializerOptions options, WriteStack& state)
at System.Text.Json.JsonSerializer.WriteCore[TValue](JsonConverter jsonConverter, Utf8JsonWriter writer, TValue& value, JsonSerializerOptions options, WriteStack& state)
at System.Text.Json.JsonSerializer.WriteStreamAsync[TValue](Stream utf8Json, TValue value, JsonTypeInfo jsonTypeInfo, CancellationToken cancellationToken)
at System.Text.Json.JsonSerializer.WriteStreamAsync[TValue](Stream utf8Json, TValue value, JsonTypeInfo jsonTypeInfo, CancellationToken cancellationToken)
at System.Text.Json.JsonSerializer.WriteStreamAsync[TValue](Stream utf8Json, TValue value, JsonTypeInfo jsonTypeInfo, CancellationToken cancellationToken)
at Microsoft.AspNetCore.Mvc.Formatters.SystemTextJsonOutputFormatter.WriteResponseBodyAsync(OutputFormatterWriteContext context, Encoding selectedEncoding)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResultFilterAsync>g__Awaited|30_0[TFilter,TFilterAsync](ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object
state, Boolean isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResultExecutedContextSealed context)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.ResultNext[TFilter,TFilterAsync](State& next, Scope& scope, Object& state, Boolean& isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.InvokeResultFilters()
--- End of stack trace from previous location ---
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeFilterPipelineAsync>g__Awaited|20_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isComplet
ed)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Logged|17_1(ResourceInvoker invoker)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Logged|17_1(ResourceInvoker invoker)
at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger)
at Microsoft.AspNetCore.Authorization.Policy.AuthorizationMiddlewareResultHandler.HandleAsync(RequestDelegate next, HttpContext context, AuthorizationPolicy policy, PolicyAuthorizationResult authori
zeResult)
at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)
The stack trace is where I found my solution, see answer below.

The stack trace indicates, that the exception occurs during JSON serialization. It is not visible from my code examples, but the IEnumerable returned is actually an IQueryable. This means the database is only called once it is enumerated, which in this particular case only happens when I try to serialize the data to send it elsewhere. At that point the context is already disposed, but not GC'd, since the IQueryable has a reference to it.
I knew of this behaviour of IQueryable, just did not see the problem here, as the return value is IEnumerable<Cat>. I basically masked the reference to a context for myself and let it escape the scope in which the context exists.
So the general answer to my question is: Make sure no references to the context leave the scope.
The concrete answer in my example above would be to change this:
public IEnumerable<Cat> AllCats => ExecuteInContext(context => context.Cats);
to this
public IEnumerable<Cat> AllCats => ExecuteInContext(context => context.Cats.ToArray());
so that the enumeration is happening inside the scope where the context exists.

LightInject Attempt to create a scoped instance without a current scope

I (noob to light inject mvc) am using LightInject MVC in my asp.mvc 4 app with great results except an occasional exception. Now I am seeing it in pre-production. The exception is: System.InvalidOperationException: Attempt to create a scoped instance without a current scope.
My app start code is:
var container = new LightInject.ServiceContainer();
container.RegisterControllers();
container.RegisterAssembly(typeof(AppDDD.RegisterMe).Assembly, () => new PerScopeLifetime());
... scoped registrations
container.EnableMvc();
I get the error with a stack trace like:
System.InvalidOperationException: An error occurred when trying to
create a controller of type 'MvcAPP.Controllers.HomeController'. Make
sure that the controller has a parameterless public constructor. --->
System.InvalidOperationException: Attempt to create a scoped instance
without a current scope. at
LightInject.PerScopeLifetime.GetInstance(Func1 createInstance, Scope
scope) at DynamicMethod(Object[] ) at
LightInject.ServiceContainer.<>c__DisplayClass40.<WrapAsFuncDelegate>b__3f()
at LightInject.PerRequestLifeTime.GetInstance(Func1 createInstance,
Scope scope) at DynamicMethod(Object[] ) at
LightInject.ServiceContainer.TryGetInstance(Type serviceType) at
System.Web.Mvc.DefaultControllerFactory.DefaultControllerActivator.Create(RequestContext
requestContext, Type controllerType) --- End of inner exception
stack trace --- at
System.Web.Mvc.DefaultControllerFactory.DefaultControllerActivator.Create(RequestContext
requestContext, Type controllerType) at
System.Web.Mvc.DefaultControllerFactory.CreateController(RequestContext
requestContext, String controllerName) at
System.Web.Mvc.MvcHandler.ProcessRequestInit(HttpContextBase
httpContext, IController& controller, IControllerFactory& factory)
at System.Web.Mvc.MvcHandler.BeginProcessRequest(HttpContextBase
httpContext, AsyncCallback callback, Object state) at
System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
at System.Web.HttpApplication.ExecuteStep(IExecutionStep step,
Boolean& completedSynchronously)
I have created a couple of small test ASP MVC projects to isolate the exception with no success.
The Controllers are scoped per instance, and all the objects with in each instance are designated PerScopeLifetime.
Is there a tweak I can make, or should I stop using PerScopeLifetime? I must have scoped lifetimes for my EF contexts.
The exception is thrown before my controllers finish constructing, so it appears.

I would like you to know that the issue has been resolved and getting the latest and greatest from NuGet should fix your problem.
Best regards
Bernhard Richter

Task`1 cannot be serialized for Web Application referencing BCL.Async

We recently deployed a newly developed pre-compiled service to our test domain and received the following error:
Type 'System.Threading.Tasks.Task`1[Domain.Infrastructure.Contracts.Configuration.DomainServices]' cannot be serialized. Consider marking it with the DataContractAttribute attribute, and marking all of its members you want serialized with the DataMemberAttribute attribute. If the type is a collection, consider marking it with the CollectionDataContractAttribute. See the Microsoft .NET Framework documentation for other supported types.
The server is Windows 2008R2 running .NET 4.0.
There has been a few Stack Overflow questions about this, but most seem to be referring to the CTP release of Async. Apparently you MUST have .NET 4.5 installed on the server in order to use this code.
Has this situation changed at all with the release of the BCL.Async NuGet package?
I was under the impression that code that was compiled with an Async compiler and includes the BCL libraries from NuGet had everything they needed to run in a .NET 4 environment.
Is it still the case that we have to upgrade the .NET runtime on the server to 4.5?
Edit: Stack Trace Provided:
[InvalidDataContractException: Type 'System.Threading.Tasks.Task`1[Domain.Infrastructure.Contracts.Configuration.DomainServices]' cannot be serialized. Consider marking it with the DataContractAttribute attribute, and marking all of its members you want serialized with the DataMemberAttribute attribute. If the type is a collection, consider marking it with the CollectionDataContractAttribute. See the Microsoft .NET Framework documentation for other supported types.]
System.Runtime.Serialization.DataContractCriticalHelper.ThrowInvalidDataContractException(String message, Type type) +1184850
System.Runtime.Serialization.DataContractCriticalHelper.CreateDataContract(Int32 id, RuntimeTypeHandle typeHandle, Type type) +787
System.Runtime.Serialization.DataContractCriticalHelper.GetDataContractSkipValidation(Int32 id, RuntimeTypeHandle typeHandle, Type type) +117
System.Runtime.Serialization.XsdDataContractExporter.GetSchemaTypeName(Type type) +85
System.ServiceModel.Dispatcher.DataContractSerializerOperationFormatter.CreatePartInfo(MessagePartDescription part, OperationFormatStyle style, DataContractSerializerOperationBehavior serializerFactory) +48
System.ServiceModel.Dispatcher.DataContractSerializerOperationFormatter.CreateMessageInfo(DataContractFormatAttribute dataContractFormatAttribute, MessageDescription messageDescription, DataContractSerializerOperationBehavior serializerFactory) +708
System.ServiceModel.Dispatcher.DataContractSerializerOperationFormatter..ctor(OperationDescription description, DataContractFormatAttribute dataContractFormatAttribute, DataContractSerializerOperationBehavior serializerFactory) +570
System.ServiceModel.Description.DataContractSerializerOperationBehavior.GetFormatter(OperationDescription operation, Boolean& formatRequest, Boolean& formatReply, Boolean isProxy) +308
System.ServiceModel.Description.DataContractSerializerOperationBehavior.System.ServiceModel.Description.IOperationBehavior.ApplyDispatchBehavior(OperationDescription description, DispatchOperation dispatch) +69
System.ServiceModel.Description.DispatcherBuilder.BindOperations(ContractDescription contract, ClientRuntime proxy, DispatchRuntime dispatch) +120
System.ServiceModel.Description.DispatcherBuilder.InitializeServiceHost(ServiceDescription description, ServiceHostBase serviceHost) +4250
System.ServiceModel.ServiceHostBase.InitializeRuntime() +82
System.ServiceModel.ServiceHostBase.OnOpen(TimeSpan timeout) +64
System.ServiceModel.Channels.CommunicationObject.Open(TimeSpan timeout) +789
System.ServiceModel.HostingManager.ActivateService(String normalizedVirtualPath) +255
System.ServiceModel.HostingManager.EnsureServiceAvailable(String normalizedVirtualPath) +1172
[ServiceActivationException: The service '/Services/Binary/Endpoint.svc' cannot be activated due to an exception during compilation. The exception message is: Type 'System.Threading.Tasks.Task`1[Domain.Infrastructure.Contracts.Configuration.DomainServices]' cannot be serialized. Consider marking it with the DataContractAttribute attribute, and marking all of its members you want serialized with the DataMemberAttribute attribute. If the type is a collection, consider marking it with the CollectionDataContractAttribute. See the Microsoft .NET Framework documentation for other supported types..]
System.Runtime.AsyncResult.End(IAsyncResult result) +901504
System.ServiceModel.Activation.HostedHttpRequestAsyncResult.End(IAsyncResult result) +178638
System.Web.AsyncEventExecutionStep.OnAsyncEventCompletion(IAsyncResult ar) +107

Okay, I'm going to take a good guess here that you're trying to expose an asynchronous WCF operation that returns a Task<Domain.Infrastructure.Contracts.Configuration.DomainServices>. While Microsoft.Bcl.Async will allow you to compile code that uses tasks, it won't provide the .NET Framework 4.5 changes to WCF that allow you to use tasks in services.
That being said, you can still use the asynchronous programming model to expose the asynchronous method to WCF, while still writing the code using the TPL. To do so, you'll have to wrap the method with APM begin/end methods. Something like this:
[ServiceContractAttribute]
public interface ISampleService
{
[OperationContractAttribute]
string SampleMethod();
[OperationContractAttribute(AsyncPattern = true)]
IAsyncResult BeginSampleMethod(AsyncCallback callback, object asyncState);
string EndSampleMethod(IAsyncResult result);
}
public class SampleService : ISampleService
{
// the async method needs to be private so that WCF doesn't try to
// understand its return type of Task<string>
private async Task<string> SampleMethodAsync()
{
// perform your async operation here
}
public string SampleMethod()
{
return this.SampleMethodAsync().Result;
}
public IAsyncResult BeginSampleMethod(AsyncCallback callback, object asyncState)
{
var task = this.SampleMethodAsync();
if (callback != null)
{
task.ContinueWith(_ => callback(task));
}
return task;
}
public string EndSampleMethod(IAsyncResult result)
{
return ((Task<string>)result).Result;
}
}

Ninject: How to not use the Ninject in "ashx" file and still not get an exception?

This is what i use to implement an Dependency Injection in my MVC3 project,
public class NinjectControllerFactory : DefaultControllerFactory
{
private readonly IKernel _ninjectKernel;
public NinjectControllerFactory()
{
_ninjectKernel = new StandardKernel();
AddBindings();
}
protected override IController GetControllerInstance(RequestContext requestContext, Type controllerType)
{
return controllerType == null ? null : (IController)_ninjectKernel.Get(controllerType);
}
private void AddBindings()
{
_ninjectKernel.Bind<IUserRepository>().To<UserRepository>().InSingletonScope();
}
}
but i have a huge problem i want to use an Generic Handler an ".ashx" to implement my logic.
But i get an exception because the httphandler is not a Controller.
here is the exception:
Server Error in '/' Application.
The IControllerFactory 'Infrastructure.NinjectFactory.NinjectControllerFactory' did not return a controller for the name 'registercustomer.ashx'.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
Exception Details: System.InvalidOperationException: The IControllerFactory 'Infrastructure.NinjectFactory.NinjectControllerFactory' did not return a controller for the name 'registercustomer.ashx'.
Source Error:
An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.
Stack Trace:
[InvalidOperationException: The IControllerFactory 'Infrastructure.NinjectFactory.NinjectControllerFactory' did not return a controller for the name 'registercustomer.ashx'.]
System.Web.Mvc.MvcHandler.ProcessRequestInit(HttpContextBase httpContext, IController& controller, IControllerFactory& factory) +422803
System.Web.Mvc.<>c__DisplayClass6.<BeginProcessRequest>b__2() +49
System.Web.Mvc.<>c__DisplayClassb`1.<ProcessInApplicationTrust>b__a() +13
System.Web.Mvc.SecurityUtil.<GetCallInAppTrustThunk>b__0(Action f) +7
System.Web.Mvc.SecurityUtil.ProcessInApplicationTrust(Action action) +22
System.Web.Mvc.SecurityUtil.ProcessInApplicationTrust(Func`1 func) +124
System.Web.Mvc.MvcHandler.BeginProcessRequest(HttpContextBase httpContext, AsyncCallback callback, Object state) +98
System.Web.Mvc.MvcHandler.BeginProcessRequest(HttpContext httpContext, AsyncCallback callback, Object state) +50
System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.BeginProcessRequest(HttpContext context, AsyncCallback cb, Object extraData) +16
System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +8971636
System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +184
Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.547
Now is the question: How do i implement the work around this bug, to me to be able to an HttpHandler and still remain using the Ninject in my project?
Thanks in advance.

Due to the HttpHandler being created by the framework and there is no hook or factory method to intercept the creation of the ashx file, ninject is not able to create this object.
However you can use service locator calls or property injection from the ashx to request dependancies from the ashx code. But as far as I know, the ashx must have a default constructor, and you can then either resolve the dependancies from inside the constructor (or anywhere really) via service locator (less preferred method) or via property injection simply like this:
public class Handler
{
[Inject]
public IService Service { get; set; }
}
EDIT: also, to tell mvc to not process the ashx file you need to add this to ignore the route:
routes.IgnoreRoute("{resource}.ashx/{*pathInfo}");

Response is not available in this context

I have problem. Locally everything works fine but in the production server it always throws exception 'Response is not available in this context'. What can be the problem? I've noticed that a lot of people experience this problem due to some changes of global.asax. Here is the code of global.asax, the part related to application start.
protected void Application_Start() {
AreaRegistration.RegisterAllAreas();
RegisterRoutes(RouteTable.Routes);
Application["SystemUser"] = TUser.GetUserByIdentifier("system").UID;
InitializeSolrInstances();
SearchIndexer.DoIndex();
StartRatingTimer();
SolrManager.RecalculateMostRequested();
}
private static void InitializeSolrInstances() {
SolrConfigurationManager.InitSolrConnection<OfferItemPresenter>(Resources.ApplicationResources.SolrServiceURL + "/offer");
SolrConfigurationManager.InitSolrConnection<SavedQueryItemPresenter>(Resources.ApplicationResources.SolrServiceURL + "/savedquery");
SolrConfigurationManager.InitSolrConnection<TopProductsPresenter>(Resources.ApplicationResources.SolrServiceURL + "/topproducts");
SolrConfigurationManager.InitSolrConnection<TopSellersPresenter>(Resources.ApplicationResources.SolrServiceURL + "/topsellers");
SolrConfigurationManager.InitSolrConnection<MostRequestedItemPresenter>(Resources.ApplicationResources.SolrServiceURL + "/mostrequested");
SolrConfigurationManager.InitSolrConnection<MostRequestedQuery>(Resources.ApplicationResources.SolrServiceURL + "/requestedquery");
}
private void StartRatingTimer() {
_LastRatingRenewedTime = DateTime.Now;
DateTime CurrentTime = DateTime.Now;
DateTime StartTime = new DateTime(2011, 1, 1);
GlobalSettings.ReIndexMainSolrCores(StartTime, CurrentTime);
Timer OfferAndUserRatingRenewerTimer = new Timer() {
/*Timer interval for 24 hours*/
Interval = 24 * 60 * 60 * 1000, Enabled = true };
OfferAndUserRatingRenewerTimer.Elapsed += new ElapsedEventHandler(OfferAndUserRatingRenewerTimer_Elapsed);
}
public void OfferAndUserRatingRenewerTimer_Elapsed(Object Sender, ElapsedEventArgs e) {
GlobalSettings.ReIndexMainSolrCores(_LastRatingRenewedTime, e.SignalTime);
_LastRatingRenewedTime = e.SignalTime;
}
I do not use Response or Request properties of HttpContext at all. Neither in global asax itself, nor within the methods to be called. Help me.
That what it shows.
`
Server Error in '/' Application.
Response is not available in this context.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
Exception Details: System.Web.HttpException: Response is not available in this context.
Source Error:
An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.
Stack Trace:
[HttpException (0x80004005): Response is not available in this context.]
System.Web.Util.HttpEncoder.get_Current() +11406684
System.Web.HttpUtility.UrlEncode(String str, Encoding e) +137
SolrNet.Impl.SolrConnection.<Get>b__0(KeyValuePair`2 input) +89
SolrNet.Utils.<Select>d__1a`2.MoveNext() +612
SolrNet.Utils.Func.Reduce(IEnumerable`1 source, TResult startValue, Accumulator`2 accumulator) +393
SolrNet.Impl.SolrConnection.Get(String relativeUrl, IEnumerable`1 parameters) +908
SolrNet.Impl.SolrQueryExecuter`1.Execute(ISolrQuery q, QueryOptions options) +195
SolrNet.Impl.SolrBasicServer`1.Query(ISolrQuery query, QueryOptions options) +176
SolrNet.Impl.SolrServer`1.Query(ISolrQuery query, QueryOptions options) +176
TebeComSearchEngine.SolrManager.RecalculateMostRequested() in SolrManager.cs:77
TebeCom.MvcApplication.Application_Start() in Global.asax.cs:101
[HttpException (0x80004005): Response is not available in this context.]
System.Web.HttpApplicationFactory.EnsureAppStartCalledForIntegratedMode(HttpContext context, HttpApplication app) +4043621
System.Web.HttpApplication.RegisterEventSubscriptionsWithIIS(IntPtr appContext, HttpContext context, MethodInfo[] handlers) +191
System.Web.HttpApplication.InitSpecial(HttpApplicationState state, MethodInfo[] handlers, IntPtr appContext, HttpContext context) +352
System.Web.HttpApplicationFactory.GetSpecialApplicationInstance(IntPtr appContext, HttpContext context) +407
System.Web.Hosting.PipelineRuntime.InitializeApplication(IntPtr appContext) +375
[HttpException (0x80004005): Response is not available in this context.]
System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +11612256
System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +141
System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +4842149`

'Response is not available in this context'. What can be the problem?
You are running this in IIS7 Integrated Application Pool mode instead of Classic mode. In Integrated mode you don't have access to the HttpResponse in Application_Start any any attempt to access it will blow.
Here's a blog post which covers a similar situation but with the HttpRequest.

After a lot of digging and looking around the SolrNet code, they don't appear to be doing anything wrong. Also, as Darin pointed out in an indirect manner, HttpUtility.UrlEncode should work fine in code without a HttpContext, such as a console application, and it does.
However, as VinayC pointed out in his comment on that answer of Darin's:
Actually, it appears to be a bug. From
reflector, actual code appears to be
"if (null != current && null !=
current.Response && ...)" where
current is current http context. Issue
here is that Response getter throws an
exception, instead of returning null
Instead of throwing that overly descriptive exception (no doubt they were trying to be helpful), they should have just returned null and let null reference exceptions happen. In this case, they were simply checking for nulls, so the exception wouldn't have happened anyway! I'll report it as a bug if it hasn't been already.
Unfortunately, what this means to you is that you have pretty much no choice but to run in Classic mode. Technically you could put the call to TebeComSearchEngine.SolrManager.RecalculateMostRequested() in a thread that you spawn in application_start and delay its execution until after the app finishes starting. As far as I know, there is no surefire way to programmatically signal the end of the application starting so, that approach may be a little messy.
If you're up for it though, you could probably get that delayed startup mechanism implemented. Compared to punishing the first visitor to the site, it doesn't seem too bad.

This was discussed about a month ago in the SolrNet mailing list.
It's a regression in ASP.NET 4, here's a mention of this bug.
A future release of SolrNet will replace System.Web.HttpUtility.UrlEncode to work around this bug. (or if you really need this, why not fork the source code and fix it?)
EDIT: I just fixed this.