With finder open, click Go->Go to folder
Manually type in
/Library/Application Support/Microsoft/Office365/User Content.localized/Startup/
Within that folder, should be folder for Word, Powerpoint, etc.
Delete any files within each Word,Powerpoint folder.
Quit and Reopen a document to verify error is gone.
Plan B:
Delete the /Startup Folder in /Library/Application Support/Microsoft/Office365/User Content.localized and reboot.
Test again.