by William Lu.
I got same error message, it is really annoying.
As you suggested, I un-tick users, then backup successfully.
Why the users interfering the backup?
I have hundreds courses in my site (Moodle2.4), only one course can't be backed up.
I know this course is the biggest course, has a lot of images in it. even without users, the mbz file is more than 2G.
Please someone help me find out the problem.
I've found several forums and Trackers are discussing about this, but no solution yet.