Q:

C# compiler: CS0121: The call is ambiguous between the following methods or properties

This is the craziest what I've seen since a Fody plugin ruined my assembly by emitting invalid code and control flow varied random at runtime... No Fody this time.
Facts:

The whole story is within one project. 
The GetMessage extension method is there since weeks... 
The issue is started since 2 hours, and I can not figure out what it is. 
There is only one GetMessage extension method.
The error message (see the pic) lists two identical method specification
Error  CS0121  The call is ambiguous between the following methods or properties: 'ComiCalc.Data.ExceptionExtensions.GetMessage2(System.Exception)' and 'ComiCalc.Data.ExceptionExtensions.GetMessage2(System.Exception)' ComiCalc.Data D:\2014Develop\.vsonline\ComiCalc\src\ComiCalc.Data\Services\UserService.cs    61

If I change both the call, both the method definition (only 2 edits in 2 places) to GetMessage2, then I got exactly the same error message just referring to the GetMessage2.
Using VS 2015

Any ideas?

and here is the single one method:
namespace ComiCalc.Data
{

    using System;
    using System.Data.Entity.Validation;
    using PluralTouch.DataAccess;
    // TODO: Move to PluralTouch
    public static class ExceptionExtensions
    {
        public static string GetMessage2(this Exception exception)
        {

            var message = exception.Message;
            if (exception is DbEntityValidationException)
            {
                message = ((DbEntityValidationException) exception).DbEntityValidationResultToString();
            }
            return message;
        }
    }
}

A:

Make sure you don't reference the output binary in your project references (i.e., the project references itself). This has happened to me in the past with Resharper (the addition of the output binary to the project references), so the extension method is both in the source and in the binary reference.

A:

Delete bin folder > open project > build solution. 

