Hi, clumpa!
I have never used Excel for Mac, but for Windows I would follow this steps if I were facing such an issue:
a) press Alt-F11 and go to the VBA editor
b) if there are any Modules present, check them out, maybe they have useful code; if not, then remove them
c) check the ThisWorkbook code, and proceed alike
d) check every Worksheet code, and do the same
d) save the workbook as .xlsx (no macros) or as .xls (versions up to 2003)
If the issue remains, you can:
a) check the existing named ranges
b) move every sheet to a clean new book
c) adjust named ranges as previously checked
d) save the workbook with no macros
If still remaining, please upload the file for checking it.
Regards!