Scheduled backup fails with "Failed to mount.." error

[cortina]

Hi,
My scheduled backups have running happily every night for several months. About a week ago they started to fail with the same log message:

| 09:28:00 PM | Info | SuperDuper!, 2.1.4 (82), path: /Applications/SuperDuper!.app, Mac OS 10.4.9 build 8P135 (ppc)
| 09:28:00 PM | Info | Started on Mon, Apr 2, 2007 at 2:28 PM
| 09:28:00 PM | Info | Source Volume: Macintosh HD, mount: /, device: /dev/disk0s3, media: WDC WD2500JD-41HBC0, interconnect: Internal ATA, file system: "Journaled HFS+", OS: 10.4.9 (8P135), capacity: 232.76 GB, used: 36.89 GB, directories: 125244, files: 568321, ejectable: NO, ACLs: Disabled
| 09:28:00 PM | Info | Target Image: /Volumes/Backup/G5 Backup/G5-backup-full.sparseimage, name: G5-backup-full
| 09:28:00 PM | Info | Copy Mode   : Smart Update
| 09:28:00 PM | Info | Copy Script : Backup - all files.dset
| 09:28:00 PM | Info | Transcript  : BuildTranscript.plist
| 09:28:00 PM | Info | PHASE: 1. Prepare to Copy Files
| 09:28:00 PM | Info | ...ACTION: Preparing Macintosh HD
| 09:28:00 PM | Info | ......COMMAND => Verifying the integrity of volinfo.database
| 09:28:00 PM | Info |       volinfo.database OK
| 09:28:00 PM | Info | ......COMMAND => Enabling permissions on Macintosh HD
| 09:28:00 PM | Info |       Refreshing Disk Arbitration ...
| 09:28:00 PM | Info | ......COMMAND => Verifying that permissions are enabled for Macintosh HD
| 09:28:00 PM | Info |       Permissions on '/' are enabled.
| 09:28:00 PM | Info | ...ACTION: Mounting G5-backup-full
| 09:28:00 PM | Info | ......COMMAND => Preparing G5-backup-full
| 09:28:00 PM | Info | ......COMMAND => Setting ownership and access modes for '/Volumes/Backup/G5 Backup/G5-backup-full.sparseimage'
| 09:28:00 PM | Info | ......COMMAND => Mounting G5-backup-full
| 09:28:05 PM | Error | load_hdi: IOHDIXControllerArrivalCallback: timed out waiting for IOKit to finish matching.

I can manually mount my backup image and run the backup but this isn't really a long term solution
Any thoughts or advice much appreciated.
TIA
Rob