I hope I have found the fix to the problem. the log for the job the last time the catalog files became corrupted had one entry about symantec temporary files being skipped. I read on a symantec forum that excluding symantec program files from the backup job may sove any problems with backing up.
I excluded the symantec program files, and the app data folders where symantec's temp files are stored, and have not had the 'corrupted catalog files' error since 8-15-08. I will continue to monitor, but hopefully this is taken care of.
Thanks for all the help