Warning “The type X in Y.cs conflicts with the imported type X in Z.dll”

Question

The main.cs of my project returns the following warning:

Warning 1 The type \'Extensions.MessageDetails\' in \'PATH\\Extensions.cs\'

Answer 1

I had this kind of issue where I had reverted from a target .NET Framework version of 4.5.2 to 4.0.

Classes in my App_Code folder had methods that called methods in other classes in that folder. When I created a standard folder I named "AppCode", and moved my classes into it, I no longer had the issue.

If I re-created the "App_Code" folder and move my classes back into it, I will have this issue again. I'm convinced it has to do with my .NET Framework version or that Visual Studio just doesn't deal well with changing it after being initially built/targeted to another version.