При попытке создать резервную копию выдало следующее:

The backup could not be completed because The following files:
./tmp
could not be read. If you want to skip unreadable files use the 'Ignore Errors' setting under 'Advanced Options' in 'Advanced Backup' or in your schedule settings profile.
No files available.
Could not complete the backup.

папка tmp в sites/default/files/tmp есть