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;
        }
    }
}