Entity Framework - Cannot convert lambda expression to type 'string' because it is not a delegate type

Question

I am using Entity Framework in my C# based code. I am running into an unexpected weirdness and am looking for suggestions.

Case 1, 2, 3, 4... Projects:
RivWorks

Answer 1

I had a similar looking problem but with Rx and in my case adding

using System;

helped. FWIW

Mess with those extension methods missing is too annoying sometimes.