We're having the same problem when attendance is included in the Backup/Import process. We're running Moodle 1.9.2.
Attendance (plugin)
Backup for 1.9 doesn't seem to be working
གྲོས་བསྟུན་འདི་བསྡམས་ཡོདཔ་ལས་ ལན་གསལ་བརྐྱབ་མི་ཚུགས་