Here is a picture of the screen:

At this point, the system was locked and I wasn't able to logout. I had to press the power button on the box to reboot. It looked like the backup continued to run, I could see both ext. hd and internal hd lights blinking, so I made sure it had time to finish. Looking at the finished backup archive files, I believe it's okay.
I was backing up /dev/sda1 to an external usb hard drive. Mga3 Gnome3 is on /dev/sda5.
Any ideas what may be causing this? Do I need to write a bug report?
Thnx.