Converting from Excel 2003 to Excel 2007

I have a complicated, multi-tabbed financial model that uses a variety of functions. In version 2003, no problem. The conversion to 2007: calculations = 0. The first problem: =SUMIF(Exp_ID_Lookup,CONCATENATE(A6,A11),Expense_Lookup)
Both named ranges are correct. I did an Evaluate Formula, and the CONCATENATE does the correct appending, but still 0 is the result.
I had a problem with another spreadsheet where I had to change a permission to open the floodgates, but that was a couple of weeks ago, and I don’t remember where it was (or if it even applies here…if so, I’d better write it down, although one would think that a global option would be available!). Could this be the solution?
Thank you for your help! This, unfortunately, is part of a time-critical project.