I have this situation too.
When I am download my backup files on Manage Backup Menu, the downloaded files didn’t containing the database, but error text instead.
This is the content of downloaded files
Warning: filesize(): stat failed for /path/to/public_html/content/backup-db/1372805295_-_novrian.info_.sql in /path/to/public_html/content/plugins/wp-dbmanager/wp-dbmanager.php on line 383