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Runtime Error after deploy asp.net webforms app in Microsoft Azure App service

I am trying to deploy in Azure WebApp service an ASP.NET Weforms.
The app runs fine locally, without any problem.
After build ends I got the error below error in web browser after i go to myapp.azurewebsites.net i
Runtime Error
Description: An application error occurred on the server. The current custom error settings for this application prevent the details of the application error from being viewed remotely (for security reasons). It could, however, be viewed by browsers running on the local server machine.
Details: To enable the details of this specific error message to be viewable on remote machines, please create a tag within a "web.config" configuration file located in the root directory of the current web application. This tag should then have its "mode" attribute set to "Off".
Here is source of Web.config file
<?xml version="1.0"?>
<configuration>
<configSections/>
<connectionStrings>
<add name="constr" providerName="System.Data.SqlClient" connectionString="server=telendar.database.windows.net; database=TrackerDB;uid=telendar;password=*****;"/>
</connectionStrings>
<location path="Admin">
<system.web>
<customErrors mode="On"/>
<authorization>
<allow roles="Administrator"/>
<deny users="*"/>
</authorization>
</system.web>
</location>
<system.web>
<compilation debug="true" targetFramework="4.5.1"/>
<sessionState timeout="60"/>
<authentication mode="Forms">
<forms defaultUrl="~/Default.aspx" loginUrl="~/AuthUser.aspx" slidingExpiration="true" timeout="60"/>
</authentication>
<authorization/>
<pages controlRenderingCompatibilityVersion="4.0" validateRequest="true">
<controls>
<add tagPrefix="ajaxToolkit" assembly="AjaxControlToolkit" namespace="AjaxControlToolkit"/>
</controls>
</pages>
</system.web>
</configuration>

You misunderstand the error message, it's telling you that your code crashed an unhandled exception and it's not allowed to show it ,it suggest you modifying the web.config to enable the details of the specific error message to be viewable on remote machines.
So what you need to do is recreate the error while you browse it on the server and then solve the problem.
However my suggestion is you could try to change your FrameWork maybe this will work for you.
If you still have other questions, please let me know.

How do I fix the custom errors?

I keep getting this error when trying to run my system
<system.web>
<customErrors mode="Off"/>
</system.web>
<system.web>
<customErrors mode="RemoteOnly" defaultRedirect="mycustompage.html"/>
</system.web>

First of all, enable the details of this specific error message by putting the "customErrors" tag in your "web.config" file like this:
<configuration>
<system.web>
<customErrors mode="Off"/>
</system.web>
</configuration>
Now you will get the exact error in your code and you can fix that specific error.
For security reasons, your code will not be shown in the browser for end user until you have not enabled CustomError mode="Off" in web.config file.

For security reasons .NET-Websites shows complete exceptions only, if you call them locally. To see the error message you have to choices:
Call the website through a browser on the Server (of course not possible, if you deploy to a Azure WebApp, but e.g. in a VM)
Add the first of your snippets (customErrors mode="Off") to your web.config. Then you'll see the complete exception even remotly over the network. My advice would be to set it back to the default setting after you've seen and fixed the error.

Customerror page in asp.net webapplication

I am developping an Asp.NET web application with visual studio 2015 and running it under IIS Express. I want to add a custom error page to it.
First, in the web.config file, I added customErrors markup under the system.web section. But it didn't seem to have any effect.
<customErrors mode="On" defaultRedirect="/Error.aspx">
<error statusCode="404" redirect="/Error.aspx" />
</customErrors>
So I added an httpErrors markup under system.webServer. And it showed me a blank page.
<httpErrors existingResponse="PassThrough" />
So I changed the above httpErrors markup by this one :
<httpErrors errorMode="Custom" existingResponse="Auto" defaultResponseMode="ExecuteURL" defaultPath="/Error.aspx">
<clear/>
<error path="/Error.aspx" responseMode="ExecuteURL" statusCode="404"/>
</httpErrors>
And it showed me the "lock violation" error. I Tried to remove ,defaultPath in the applicationHost.config file, rebooted the computer, but the same error appears
Even in Global.asax, the Application_Error is not fired in the case of some error like 404.
Does someone have any clue ?
Edit :
I tried to do the same thing in a new solution :
So I created a new web application - Blank webforms template. Same result.
But when I created a new web application - Blank MVC solution, it worked.
Is there any difference in the config between webforms and mvc? Is someone else have the same issue whith the webforms template ?

I was able to redirect to error page. I tried this in my current MVC project. Below is excerpt of what i did
Used existing error page in my solution under Views/Shared/Error.cshtml
Used your custom errors parameters
<customErrors mode="On" defaultRedirect="~/Views/Shared/Error.cshtml">
<error statusCode="404" redirect="~/Views/Shared/Error.cshtml" />
</customErrors>
Threw 404 purposefully in my Index.cshtml
#Response.StatusCode=404
#Response.End()
Hint: Please try to see the path and how you are testing 404 error

Server Error in '/' Application in c#

<system.web>
<customErrors mode="off" defaultRedirect="~/Contents/error.aspx">
</customErrors>
<sessionState mode="InProc" cookieless="UseCookies" timeout="20">
</sessionState>
</system.web>
Added system web.config code.i changed to
customErrors mode="on".still same error.please check these code as well. can anyone help me to solve this error.

If you read the error, it tells you that the attribute needs to be "RemoteOnly, On, Off". You need to change the attribute mode="off" to mode="Off".

Web Config problem in asp.net. i am using vs 2010. my web.config is given below

<?xml version="1.0"?>
<configuration>
<appSettings>
<add key="ConnectionInfo" value="server=127.0.1.1;database=Info_mgmt;Integrated Security=SSPI"/>
</appSettings>
<connectionStrings>
<add name="Info_mgmtConnectionString" connectionString="Data Source=daffodils\sqlexpress;Initial Catalog=Info_mgmt;Integrated Security=True" providerName="System.Data.SqlClient"/>
</connectionStrings>
<system.web>
<compilation debug="true" targetFramework="4.0">
</compilation>
<!--
The <authentication> section enables configuration
of the security authentication mode used by
ASP.NET to identify an incoming user.
-->
<authentication mode="Windows"/>
<!--
The <customErrors> section enables configuration
of what to do if/when an unhandled error occurs
during the execution of a request. Specifically,
it enables developers to configure html error pages
to be displayed in place of a error stack trace.
<customErrors mode="RemoteOnly" defaultRedirect="GenericErrorPage.htm">
<error statusCode="403" redirect="NoAccess.htm" />
<error statusCode="404" redirect="FileNotFound.htm" />
</customErrors>
-->
<pages controlRenderingCompatibilityVersion="3.5" clientIDMode="AutoID"/></system.web>
<!--
The system.webServer section is required for running ASP.NET AJAX under Internet
Information Services 7.0. It is not necessary for previous version of IIS.
-->
</configuration>
Error:
Configuration Error
Description: An error occurred during the processing of a configuration file required to service this request. Please review the specific error details below and modify your configuration file appropriately.
Parser Error Message: Unrecognized attribute 'targetFramework'. Note that attribute names are case-sensitive.
Source Error:
Line 7:
Line 8:
Line 9:
Line 10:
Line 11:
Source File: D:\Infopass\Infopass-Web\Infopass-Web\web.config Line: 9

The targetFramework attribute is specified on the <compilation> element under <system.web>. I have seen that error message when running sites in IIS 7.5 using ASP.NET 2.0 instead of ASP.NET 4.0. If this site is in IIS, then check the Application Pool the site is running under to make sure the Application Pool is using the .NET 4.0 Framework (instead of .NET 2.0 Framework).
Similarly, if you are attempting to run the site from the default web server in Visual Studio and you are seeing this error, you'll want to make sure the Target Framework for the project is set to .NET Framework 4.0 (under Properties > Build > Target Framework).

You need to set your application to use .Net 4.0 in IIS.