A possible failure can result from deleting a value in the Excel network document using the [Del] key. In this case, the cell may still be evaluated, albeit with an empty result, or NaN. Any occurrence of NaN will trigger the error message in the figure below.
Locate and correct the corrupted data cell. If no data cells are obviously blank, a cell in an empty row or column could be causing the issue. Delete the rows surrounding all data by selecting the entire rows and columns and using ‘Delete’ in the right-click menu.