Vista Backup Failing : 0x80070002 Error Code - Colin

My PC tried to run its weekly backup tonight, but failed. This is the first
time this has happened - the last successful backup was on 4th February
2008.

Running Vista Home Premium, and I back up my C Drive files onto a second
internal hard drive.
This drive has two partitions (Z and F). Z is just used for backups, and
there is still 176GB free out of 238GB on the partition.

The error occurs only a minute or so into the backup attempt. The error
message that comes up is:

'The backup did not complete successfully.
An error occurred. The following information might help you resolve the
error:
The system cannot find the file specified. (0x80070002)'

Googling the problem shows others have had it, but no definitive resolution
is given.

I have tried deleting the backup task from task manager, moving the existing
backup volumes into a temporary sub directory, and creating a whole new
shadow backup from scratch in the root of Z. However, even this fails with
the same error. I'm beginning to suspect a registry problem.

Is this a known Vista bug? Will I have to wait for SP1 to resolve it?

Thanks.

Colin