that this is due to accumulating cell format IDs over time, when Excel documents have been used and updated over and over again. Microsoft says that this can be prevented in new Excel files by keeping Excel up to date, but does not give an automatic solution this way. Instead, when the problem is seen, we have to run a utility on the Excel file throwing the error. I found a very small binary in the SkyDrive account referred-to in the article above, called XLCleaner; this works quite well. I did not choose any of the checkboxes in my testing, they look like they might alter spreadsheet contents, and they did not appear to be necessary.