Excel 2007 : sumif formula using cell reference

I am using the SUMIF function in a number of worksheets within 2 linked workbooks. Several spreadsheets have columns for monthly expenditures which are forecasts that turn into actuals when the month is complete. A column to the right is the total of the Year to Date actuals and has a SUMIF statement that adds each month if it is less than or equal to a value (# of months included in actuals) in one of the workbooks. This way the formulas in all spreadsheets can change each month by changing only one number. The formula works if I put in the actual number but not if I put in the cell reference where the number sits. Any ideas what I'm missing?

without the actual formula, hard to give exact answer, but you need to adjust it to something like:

=Sumif(X1:X100,">"&A1,Y1:Y100) where the cell reference is outside the " "

or

=Sumif(X1:X100,A1,Y1:Y100) where A1 does not have quotes around it...