May 26 2019 06:44 AM
Excel Office 365 (older files) will no longer open
All have the .xlsx extension
I get error message" that the file format or extension is not valid or file is corrupt"
What can I do to resolve this?
May 26 2019 07:57 AM
It usually works if you close Excel and start again.
Note: Check the task manager (process tab) to verify that Excel (and Microsoft.Mashup processes) are really closed.