Fix Visual Studio 2013 Error List

Question

This problem has been bugging me for some time now. I can build the project and the code looks correct but no matter what I do, I still get errors in the errors list (which infact stops some features working inside visual studio). I can still run the project completely fine.

And as an example here is ConnectionState, which clearly shows it being inside the namespace!

namespace Versioning 
{   
public enum ConnectionState     
{       Connected,      Disconnected    }
...
}

Side notes:

1) I have tried explicitly adding the assembly. i.e. xmlns:helpers="clr-namespace:MyProject.Helpers;assembly=MyAssembly"

2) This is not on a shared network drive.

3) I have rebooted visual studio