Excel 2003

I've created a simple user function in VBA. It uses data in a cell to
calculate an answer. It works fine, except when I change the input data,
the function doesn't recalculate. All other recalcs work on the
spreadsheet.

I have checked that auto recalc is on, and but even when I press F9, the
recalc doesn't work. I have to edit the cell formula or copy and paste the
formulae again in order to recalc.

Any thoughts on resolving this?