GoldenTomato
A tip to help you resolve issues.
Search the Forums on the error or message phrase
ie in this case do a search of the Forums (see link at top of Forums) on
Backup terminated: pre-backup failed - status: 256
You will get many search results, one of which located here
http://forums.contribs.org/index.php/topic,39824.msg182986.html#msg182986suggested this
Search /var/log/messages starting from line "Processing event: pre-backup" for the action script that causes the error.
If you do not understand what to do about whatever you find, then report that information from the log file back here.