We came across 2 bugs in The Budget Wizard for Excel function recently. Partnersource was being very unreliable so we finally had to give up and ask for help. This issue does occur even with SP2 in GP 10.
If you create an Excel budge file using the wizard and then try to import it back in an error message occurs indicating that the number of columns in the sheet doesn't match the number of columns in GP. Even if you export a blank budget sheet and try to import it immediately back in, it won't work.
The items to review to fix this are:
1) You need 3 lines at the top of the sheet. Two that can be blank and the column header is the third line.
2) If you have renamed your periods to something like January, Feb, etc. they come in to the budget file as dates. We didn't have any success renaming these as text. What did work was renaming the headings in the Excel sheet as Period 1, Period 2, etc. You don't have to rename them in GP, just in the Excel sheet columns. Interestingly, changing the column titles to text January, February, etc. didn't solve the problem either. It had to be non-date related.
Our issue was number 2 on the list. It was really frustrating to export a budget and not be able to import it right back in and the error message was really no help. But now we have an answer and so do you.