Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
When do you get the error message? Is it while opening Excel application or while opening any saved spreadsheet.
Does this happen with all the Excel files are only with a particular Excel file?
If it happens only with a particular file, what is the extension of that file?
Check in application safe:
Press ‘Windows key + R’ and in the window type ‘Excel /safe’ without quotes and click ok. Check for the error message, if you do not get any error then it is due to add-ins in Excel. Follow the link and disable the add-ins from Excel.
http://office.microsoft.com/en-us/help/HA100341271033.aspx
Also check the article below, might be helpful.