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Intermittent "The operation timed out" error on production server

I have a web API(service) whose target framework is .net core 2.0.
This service is calling a custom identity server 4 endpoint using HttpClient by using the 'using' statement. This call always works fine on the development/UAT server.
But on all production servers, it fails intermittently and throws the following exception:
One or more errors occurred. (An error occurred while sending the
request.) Exception: System.AggregateException: One or more errors
occurred. (An error occurred while sending the request.) --->
System.Net.Http.HttpRequestException: An error occurred while sending
the request. ---> System.Net.Http.WinHttpException: The operation
timed out at
System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at
System.Threading.Tasks.RendezvousAwaitable`1.GetResult() at
System.Net.Http.WinHttpHandler.d__105.MoveNext() ---
End of inner exception stack trace --- at
System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task
task) at
System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1.ConfiguredTaskAwaiter.GetResult()
at
System.Net.Http.HttpClient.d__58.MoveNext()
--- End of inner exception stack trace --- at System.Threading.Tasks.Task`1.GetResultCore(Boolean
waitCompletionNotification) at Get(String a, String b)
I went through related stack-overflow posts, some suggested making HttpClient static as it might throw socket exhaustion error. But I am not getting that error either I am able to reproduce this issue on a development server. I created a console application and called this service 64k times, but still, it worked properly.
How to stop outbound HTTP connections from timing out
Asp.net Core HttpClient has many TIME_WAIT or CLOSE_WAIT connections
Can someone please tell me, what can be the reason for this intermittent error only on the production server or is there any way I can reproduce this issue on the dev server. I have tried by making many calls to service, but still unable to reproduce the error.

Creating a thumbnail from MP4 video crashes on shared hosting but working fine locally

i am working on a web page to upload MP4 video and getting a thumbnail from the video
i am using NReco FFMpeg Converter to achieve this . it is working fine locally but upload it on a shared hosting it crashes at ffMpeg.GetVideoThumbnail
string VideoUrl = dataMediaUrl.ImageUrl;
string extension = VideoUrl.Split('.')[VideoUrl.Split('.').Length - 1];
var ffMpeg = new NReco.VideoConverter.FFMpegConverter();
string thumbnailJPEGpath = Server.MapPath(VideoUrl.Replace("~/upload/MediaGallery/", "~/upload/MediaGallery/Thumb_").Replace("." + extension, ".jpg"));
ffMpeg.GetVideoThumbnail(Server.MapPath(VideoUrl), thumbnailJPEGpath);
dataThumbUrl.ImageUrl = VideoUrl.Replace("~/upload/MediaGallery/", "~/upload/MediaGallery/Thumb_").Replace("." + extension, ".jpg");
This is the error I am getting:
Server Error in '/' Application.
This program is blocked by group policy. For more information, contact your system administrator
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.ComponentModel.Win32Exception: This program is blocked by group policy. For more information, contact your system administrator
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:
[Win32Exception (0x80004005): This program is blocked by group policy. For more information, contact your system administrator]
System.Diagnostics.Process.StartWithCreateProcess(ProcessStartInfo startInfo) +1889
System.Diagnostics.Process.Start() +119
System.Diagnostics.Process.Start(ProcessStartInfo startInfo) +49
NReco.VideoConverter.FFMpegConverter.ConvertMedia(Media input, Media output, ConvertSettings settings) +1163
NReco.VideoConverter.FFMpegConverter.GetVideoThumbnail(String inputFile, String outputFile, Nullable`1 frameTime) +155
Admin_MediaGalleryVideoUpload.InsertButton_Click(Object sender, EventArgs e) +591
System.Web.UI.WebControls.Button.OnClick(EventArgs e) +9782698
System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +204
System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +12
System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +15
System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +35
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1639
Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.7.3394.0

Your problem is that part of the code (probably inside of one of the methods you call):
System.Diagnostics.Process.StartWithCreateProcess(ProcessStartInfo startInfo)
If it execute a process on a remote machine the user that execute it need to have the permissions to execute programs on it (not granted by default).
To help you more we need to know the source code of method where StartWithCreateProcess is called ( NReco.VideoConverter.FFMpegConverter.GetVideoThumbnail(...)).
EDIT:
Googling a bit seems that NReco is an external library, i suggest to open a ticket to their support.

Sequence contains no elements server side

I am developing a Asp.net MVC web application and have been deploying to a web server for a few months now. Just recently I have experienced a new error that confused me. Upon publishing my application, and loading up the website, I get the following error message:
Sequence contains no elements
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: Sequence contains no elements
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: Sequence contains no elements]
System.Linq.Enumerable.First(IEnumerable`1 source) +514
System.Linq.Queryable.First(IQueryable`1 source) +330
LabSys.MvcApplication.Application_AuthorizeRequest(Object sender, EventArgs e) +1261
System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +92
System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean&completedSynchronously) +165
I am very confused, because the application runs perfectly on localhost, without any issue or error message. I also checked my database, and it is also connected and validated to the server. So there should be no error.
Thanks for any help in advance!

Check in your code to make sure FirstOrDefault() or SingleOrDefault() is used instead of using any of these: First() or Single().
When you get theLINQ Error "Sequence contains no elements", this is
usually because you are using the First() or Single() command rather
than FirstOrDefault() and SingleOrDefault().
Sequence contains no elements?

wcf client reporting SSL exception only on one occasion

Our WCF client normally invokes a web service. All deployments of the client invoke the same web service. In most deployments it makes the call without any issues, except in one instance it reports the following exception:
System.Net.Http.HttpRequestException: An error occurred while sending the request. ---> System.Net.WebException: The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel. ---> System.Security.Authentication.AuthenticationException: The remote certificate is invalid according to the validation procedure.
at System.Net.TlsStream.EndWrite(IAsyncResult asyncResult)
at System.Net.PooledStream.EndWrite(IAsyncResult asyncResult)
at System.Net.ConnectStream.WriteHeadersCallback(IAsyncResult ar)
--- End of inner exception stack trace ---
at System.Net.HttpWebRequest.EndGetResponse(IAsyncResult asyncResult)
at System.Net.Http.HttpClientHandler.GetResponseCallback(IAsyncResult ar)
--- End of inner exception stack trace ---
What could be different with this one installation?
We tested the URL that the client uses to make the call to the web service in the browser. The web service returns a response ok in Firefox but not in IE.

Have you seen this article yet? It contains fairly good tips for troubleshooting these issues: http://blogs.msdn.com/b/jpsanders/archive/2009/09/16/troubleshooting-asp-net-the-remote-certificate-is-invalid-according-to-the-validation-procedure.aspx?Redirected=true
For example, you'll need to check that the particular machine has all the root and intermediate certificates properly deployed.

I found the solution - there was a new web service server certificate installed with SHA256 and Windows 2003 Server requires a hotfix to support it:
http://support.microsoft.com/kb/938397

Security Exceptions while initializing Nlog event log target

I'm using NLog in my ASP.NET application hosted on IIS and Windows server 2003. When I run the code on my develop machine, everything is Okay. But when I deployed the code to the server. The initialization of NLog target will cause an security exception:
Security Exception
Description: The application attempted to perform an operation not allowed by the security policy. To grant this application the required permission please contact your system administrator or change the application's trust level in the configuration file.
Exception Details: System.Security.SecurityException: Requested registry access is not allowed.
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:
[SecurityException: Requested registry
access is not allowed.]
System.ThrowHelper.ThrowSecurityException(ExceptionResource
resource) +51
Microsoft.Win32.RegistryKey.OpenSubKey(String
name, Boolean writable) +7462217
System.Diagnostics.EventLog.CreateEventSource(EventSourceCreationData
sourceData) +366
NLog.Targets.EventLogTarget.CreateEventSourceIfNeeded()
+637 NLog.Targets.EventLogTarget.InitializeTarget()
+40 NLog.Targets.Target.Initialize() +264
NLog.Config.LoggingConfiguration.InitializeAll()
+233
Does anyone when what should I do in order to give the application proper permission? Thanks!

Okay, I got it. Network Service account does not have permission to read/write the event log. That's why the exception thrown.

I have run my application once as administrator to create the appropriate rules in the EventLog.