Ok. Fixed the issue with the mount. NFS is now mountable from every specified NFS client without any problems. It also works on the console from the debian machine XOCE is running on. But (as always there is a but) backup still does not work. I have a new error now:
no such remote 81601679-0c37-4a0d-874c-818b3c576df3
what does it want from me?
EDIT: huh. Just removed the backupJob and made a new one. Now everything works... This XO is really confusing some times