Most likely it could be because of a Formula or a Named Ranges, although there are other possibilities as well.
1. How to identify the problematic Formula.
Goto the menu "Edit > Find" ( or press
2. How to identify the problematic Named Range.
Look for a Named Range that is linked to an external Workbook.
I do it this way.
go to an empty portion of the worksheet.
go to the Menu "Insert >> Name >> Paste" and click "Paste List".
Now you can manually search or use the method 1 to identify.
For the full info, click here.