Not recognizing Excel sheets

After setting up my WD My Passports on my PC, I thought all was well.  It initially backed up all my files.  I have one backup just for pictures and the other for everything else.

When I tried to save an Excel sheet that I had added to, it doesn’t recognize the extension.

What can I do?

Check the link for supported files.

If still not working, do a manual copy paste back up.