Backup permissions prob with NAS drive


Network newbie here. I've got a Buffalo Linkstation 120G NAS drive attached to my router, and am trying to back up to it from my OS X.3.9 iMac, using the .Mac Backup utility. The files I am trying to backup are Office docs in the main, from my daughter's user account on the Mac.

About 40% of the files I try to back up are 'skipped' because there appears to be some permissions problem. I've changed all the file permissions in the iMac folder to 'Read and Write' even for guests, and this makes no difference.

Anyone come across a solution for this type of problem?