Database Query Failure

[Todd]

I am getting the following error when running a full backup of one of my 2005 SQL databases.

AOFO: Initialization failure on: "SERVER". Advanced Open File Option used: Microsoft Volume Shadow C...
Snapshot provider error (0xE0008492): Database Query Failure. See the job log for details.

I have never got a full backup to run on this database. Differential backups on the other hand complete successfully. Where should I start looking for the problem?

Thanks,

Todd