For that infuriating "too many cell formats" error, I've found that sometimes, though not always, if you save down to Excel 97-2003 it seems to fix it. But it's hit or miss. It can also destroy everything.
Another more involved process is as follows, however, is also with risk….
This can completely destroy your excel file by removing ALL formatting, formulas, EVERYTHING and leave you with just raw useless text so SAVE another copy!!!!!!
Under the "Resolution" section click on "Remove Styles Add-In"
***Note, excel should be open***
Click on "Downloads" tab
Download: "RemoveStyles.xlam for Excel 2007 and newer"
You will get a download notification, and should click "Open"
You should now see a new button on the excel Home tab
****Highly HIGHLY recommend saving another copy of your excel file before proceeding in case something goes haywire you can still go back to your original file*****
Click on the "Remove Styles" button, and hope for the best.
-------
You know you've downloaded and installed the Remove Styles add-in before but now the button isn't showing on the home tab.
Go to File > Options > Add-Ins > Manage: Excel Add-Ins and click Go…
You will see a list of Add-Ins and likely the Remove Extra Styles is "checked". You will want to "uncheck" Remove Extra Styles" then click OK, then go back in using the above steps and "check" Remove Extra Styles and click OK. This should cause the button to reappear on the Home tab.
-----------------------------
OTHER THINGS TO TRY
Below ideas are not "confirmed" fixes, but things I have tried in the past that have seemed to help resolve the error
-Remove unnecessary conditional formatting: Home tab > Conditional Formatting drop down > Clear Rules from Selected Cells (or you can Clear Rules from Entire Sheet)
-Remove unnecessary drop down lists from Data Validation: Select applicable cells > Data tab >
