Now I disabled the files backup and will see whats happen.
I think I've done all settings right, but since a few days backup genie will not work... Whats the matter?
2.) Backup folder are set to 777
3.) I've already change the memory limit a few times before to find the problem.
Yesterday evening I change the backup folder to another destination on the server, outside the oxwall installation folder. Now the backup works correctly!