Error 18 in Time Machine....

[iith096]

Hello all,

Recently I have been having a problem getting my Time Machine backups to complete. I continue to receive the following error in the system.log:

Oct 20 09:32:25 admins-mac-pro /System/Library/CoreServices/backupd[14338]: Backup failed with error: 18
Oct 20 10:32:20 admins-mac-pro /System/Library/CoreServices/backupd[14419]: Starting standard backup
Oct 20 10:32:20 admins-mac-pro /System/Library/CoreServices/backupd[14419]: Volume at path /Volumes/Drobo Backup does not appear to be the correct backup volume for this computer. (Cookies do not match

My current backup strategy is:

System:
2.8ghz Quad Core Mac Pro, 8GB Ram, 3 internal hard drives.

Drives:
1: Boot: 500GB WD Green Drive.
2: Super Duper backup drive. 500GB WD Green Drive. This is doing a daily backup mirror of my first boot drive above.
3: 1TB WD Green Drive which holds my Time Machine backups along with backups of the contents on my external Drobo disk array. Currently, 500+GB of data out of a total 2TB of space.

Every night in addition to the daily Super Duper backup of my boot drive to the second internal hard drive, I also do a backup of the contents on my external Drobo disk array to my third internal hard drive. As stated, my Time Machine backups are also saved to this third internal drive along side with my other data.

All backups work as requested with zero errors. However, every morning exactly after my Drobo backup completes, my Time Machine backup begins to fail with the same "error 18" error. I have to manually "remove" my existing Time Machine disc selection in settings and then re-choose it again and my Time Machine backups start up again with no further problems.

Has anyone else seen this error? Any luck resolving it? Per the Super Duper help files, it states that I can have Super Duper backup to and save my data along with an existing Time Machine backup and Super Duper preserves it.

Thanks all for your help and sorry for the long post.

Carlos.