Vista - Vista backup shadow copy error 0x8004230F

I have Vista's automatic backup feature set to do an incremental backup each evening at 9 pm, when I am not usually using the machine. However, about one time in 3 it fails with an "unexpected error" as above, in the "creating shadow copy" stage.
I am aware that a re-boot will fix this and allow backup to run.
However, I already shut down my computer every night so am unwilling to do an additional restart each evening shortly before the backup is due to run.
Is there any way to resolve or prevent this error without restarting the computer?
I've tried re-starting the VSS service after the failure and then re-trying the backup, but it always fails with the same error and will not run again until the machine has been restarted.

Did you try looking in the error log?
Search on the error code wasn't very helpful as everyone reboots to fix it.

It's been my experience that backup software is the least likely to work as expected. Esp. stuff that comes with the OS or HD. Try a 3rd party program. Do research like going to the support forums for the particular products and see which ones seem to work well on configurations closest to what you have. You should get a good idea after one or two days of looking around. The System Snapshot type programs are getting cheaper. You should be able to find something good under $50.

I did look in the Event Viewer, where I saw these errors:

VSS Event ID 12293
Volume Shadow Copy Service error: Error calling a routine on a Shadow Copy Provider {b5946137-7b9f-4925-af80-51abd60b20d5}. Routine details PreFinalCommitSnapshots({f624496a-047d-4685-9d2c-5a9dbb5fc2ef}, 1) [hr = 0x8000ffff].
Operation:
Executing Asynchronous Operation
Context:
Current State: DoSnapshotSet

Immediately Followed by:

Windows Backup Event ID 4100
File backup failed because a shadow copy could not be created. The system might be low on resources. The error is: The shadow copy provider had an unexpected error while trying to process the specified operation. (0x8004230F).

My system isn't low on resources to the best of my knowledge. I have 4 GB memory and 220 GB free on my C drive.

I was considering Acronis True Image, but when I did some research in various forums I found it has a reputation for being flaky (to say the least) with Vista.