Mountain Lion Compatibility

Still having problem with my ReadyNAS Duo and ML...

If I disable AFP under standard file protocols and directly re-enable it will work once:

Starting manual backup Attempting to mount network destination URL: afp://ReadyNAS@nasse.local/ReadyNAS Mounted network destination at mount point: /Volumes/ReadyNAS using URL: afp://ReadyNAS@nasse.local/ReadyNAS Disk image /Volumes/ReadyNAS/JockesMBP.sparsebundle mounted at: /Volumes/Time Machine Backups Backing up to: /Volumes/Time Machine Backups/Backups.backupdb Using file event preflight for Macintosh HD Will copy (752.2 MB) from Macintosh HD Found 23513 files (1.27 GB) needing backup 2.9 GB required (including padding), 312.82 GB available Copied 31698 files (1.02 GB) from volume Macintosh HD. Using file event preflight for Macintosh HD Will copy (122.1 MB) from Macintosh HD Found 993 files (122.1 MB) needing backup 1.53 GB required (including padding), 311.61 GB available Copied 2723 files (145.3 MB) from volume Macintosh HD. Created new backup: 2012-08-31-090343 Starting post-backup thinning No post-back up thinning needed: no expired backups exist Backup completed successfully. Ejected Time Machine disk image: /Volumes/ReadyNAS/JockesMBP.sparsebundle Ejected Time Machine network volume.

No problems there right? Well, next backup generates this:

Starting manual backup Backup failed with error: 19

Why can it work only once?? I have searched and searched but it seems like no one else has this problem after upgrading to ML. I have two different Mac's at home and both behaves the same after the upgrade...