When I tried to place backups in the super directory of my website (next to the "HTML" directory used by the webserver), this nifty tool was not able to create a backup. The default location worked fined.
A little digging showed that the backup directory needs to have the webserver "apache" as the owner. CHOWNed that property and things are working fine now. Simply having apache be a member of the owner group did not suffice.