MethodAccessException on Task.CompletedTask property

Question

I am working on a small wpf application and one of the users is getting the following exception:

System.MethodAccessException: 
Attempt by method "xxx.HttpConfirmation.Invoke()" to access method "System.Threading.Tasks.Task.get_CompletedTask()" failed.
at xxx.HttpConfirmation.Invoke()
at xxx.RequestPipeline.<ProcessQueuedRequests>d__11.MoveNext()

According to MSDN documentation, such exception is thrown in the following situations:

A private, protected, or internal method that would not be accessible from normal compiled code is accessed from partially trusted code by using reflection.
A security-critical method is accessed from transparent code.
The access level of a method in a class library has changed, and one or more assemblies that reference the library have not been recompiled.

Task.get_CompletedTask() is public since its introduction and I am also not using reflection to access the property.

I also don't think that there is a problem with code security/transparency since only one user is having this issue.

The exception is thrown at the Task.CompletedTask line:

public class HttpConfirmation
{
    public static Task Invoke()
    {
        using (var client = new WebClient())
        {
            try
            {
                // Send the request and don't wait for the response.
                client.UploadStringTaskAsync("http://sampleUrl.com", string.Empty);
            }
            catch
            {
                // ignore
            }
        }

        return Task.CompletedTask;
    }
}

Any ideas on what may cause the exception?

Please read up how to create a [mcve]. We cannot guess what code you are using and in what situation. — Camilo Terevinto, Jan 30 '18 at 14:03
added the code, I am not able to reproduce the issue on any machine though. — MartinK, Jan 30 '18 at 14:24
Can you reduce the code further to a single static method that takes no arguments? What .NET Framework version is installed and what version are you targeting? — usr, Jan 30 '18 at 14:33
The program is targeting .NET 4.6. The only thing I have is the exception stack trace, I don't have any other information about .NET or OS version of the customer. — MartinK, Jan 30 '18 at 14:49

score 1 · Accepted Answer · answered Feb 01 '18 at 10:54

1

The problem was that the customer had .NET 4.5.2 installed and the program targeted .NET 4.6. Though I still have no clue as to why exactly System.MethodAccessException was thrown as none of the 3 documented situations for throwing this exception did happen.

answered Feb 01 '18 at 10:54

MartinK

45
8

The documentation is incomplete. That exception is expected when an assembly references a method that does not exist. In that earlier framework that method is simply not there. – usr Feb 04 '18 at 10:56

MethodAccessException on Task.CompletedTask property

1 Answers1