Time machine makes Null backups

My backup drive recently failed. I've now replaced the drive, but I am unable to get time machine to make a backup. It seems to start, says its preparing, then a few seconds later says "Finishing backup" and stops. The log contains the following entries...

9/2/08 21:57:01 /System/Library/CoreServices/backupd[1597] Backup requested by user
9/2/08 21:57:01 /System/Library/CoreServices/backupd[1597] Starting standard backup
9/2/08 21:57:01 /System/Library/CoreServices/backupd[1597] Backing up to: /Volumes/Time Machine Backups/Backups.backupdb
9/2/08 21:57:02 /System/Library/CoreServices/backupd[1597] No pre-backup thinning needed: 100.0 MB requested (including padding), 930.97 GB available
9/2/08 21:57:12 /System/Library/CoreServices/backupd[1597] Copied 1 files (6 KB) from volume Sol HD.
9/2/08 21:57:14 /System/Library/CoreServices/backupd[1597] Starting post-backup thinning
9/2/08 21:57:14 /System/Library/CoreServices/backupd[1597] No post-back up thinning needed: no expired backups exist
9/2/08 21:57:14 /System/Library/CoreServices/backupd[1597] Backup completed successfully.