Time Machine will back up to external HD since Catalina Update.
I just updated to Catalina. I have one external hard drive plugged in via USB for Time Machine. Since the update to Catalina when I try to backup Time Machine freezes at "preparing for backup". It never gets past this initial message. I see the external HD in the finder and I can open up Time machine on the external and go back in time and restore files. I just cannot make a new backup since the update.
I have a second external HD that I rotate with the first external HD for Time Machine. This drive was not attached to the MAC when I update to Catalina. Now when I attach it the computer says "this disk unreadable." I tried Disk Utility with no results.
My trouble shooting has included. Rebooting, turning off computer entirely, removing every thing that was plugged into the USB ports except the external HD, I have tried them in different ports . I even tried them on another MAC running Snow Leopard. Same results.
I rebooted in Recovery Mode then I ran Disk Utility. I ran it on the source as well as the the destination drive. This brilliant idea worked !
My issue has been resolved . Thanks for both ideas.