Excel files in Time Machine are corrupt
None of the Excel files in my Time Machine backups will open. I get a message box: "Excel could not open [file name] because some content is unreadable. Do you want to open and repair this workbook?" Then, if I click "open and repair", the message box reads: "the workbook cannot be opened or repaired by Microsoft Excel because it is corrupt."
My Word files in backup will open normally.
I would appreciate some assistance in troubleshooting this. Many thanks!
iMac, OS X El Capitan (10.11.1), Microsoft Office for Mac 2011