Yesterday all my Excel workbooks will not open without hitting "Grant Access". When doing that, I get an "Alert" telling me that either the file format or file extension is not valid and the workbook will not open.
This affects ALL of my Excel workbooks.
Where do I start looking for the cause of this issue
I did - beyond my ability. Logged into Applesupport.com and talked to a teckie who fixed the problem. Had to do with many of my documents losing their read & write permissions. They got reset as read and write and problem was solved@Wandamartini