A problem that may occur with the Report Wizard if you try to group by a date field. Because dates are stored as numbers in Excel, your dates will appear as numbers. Then when your inner NL function tries to reference the date for its filter, it will see a number instead of a date so it will not return any results. This problem can be fixed by inserting a new column next to the date column and doing an Excel TEXT function to turn the number into a date (something like =TEXT(F5,"MM/DD/YYYY")). Then you have to update the cell reference in the column that is copied down that the inner NL function references to point to the text date.
One other problem may occur with the field cache dropped by the Report Wizard if you try to add onto a report created by the wizard.