Not very descriptive I'm afraid:
Unable to complete backup. An error occurred while copying files to the backup volume.
I just searched the web and a few people are having this problem, but I can't find a link to solution.
I'm going to try via a USB cable instead of FW and see if that fixes it.
MacBook Pro, 500 GB La Cie drive worked fine up until the upgrade.
Rgds
Gday