Excel found a problem with one or more formula references in this worksheet. Check that the cell references, range names, defined names, and links to other workbooks in your formulas are all correct.

Discover 13 essential Excel fixes to solve formula errors, formatting glitches, and data issues. Streamline tasks & create dynamic visuals ...

If you can't click on cells in your Excel workbook, try reopening the workbook or click on another window and then back to Excel; if that doesn't work, follow these methods.