Data validation between workbooks

I am having some trouble using data validation between workbooks. I am trying
to pass this formula through data validation:
=indirect(vlookup(A1,GradeLookup,2,0)).

I have created named ranges(with the same names) in both workbooks. I have
also created a lookup range in the source file called "GradeLookup". I
cannot get the lookup function to work correctly. I know that I can us a
Vlookup in the same workbook, but can I use this function between workbooks?

If I hardcode one of the ranges output file (data validation) it passes the
correct information, so I think that the problem is the Vlookup.

I have refered to the Contextures website. However, I cannot find the
answer to my question.

Thanks in advance!