EF 4 error – Cannot convert lambda expression to type ‘string’ because it is not a delegate type

I’m involved in some EF 4 development now and I ran into an error I couldn’t understand. Fortunately I wasn’t the first to experience this so it could be solved. However this is an example of an error description that could have been clearer.

The error was:

Cannot convert lambda expression to type ‘string’ because it is not a delegate type

The solution was:

Add the System.Linq using statement to the code……

I found the solution here.