variable '' of type '' referenced from scope '', but it is not defined

Question

Well, the following code is self-explaining; I want to combine two expressions into one using And operator. The last line causes rune-time the error:

Answer 1

Thanks everybody collaborated.

As @dasblinkenlight pointed out the two parameters in the two expressions are not the same. Reason? Well, it is the compiler trick. When compiling, it creates a class for each expression and name each parameter something like xxx1, xxx2,... completely different from the original names.

And the answer for .Net 4.0+:

How to Combine two lambdas