What is error 2155348001???

Hello,

I've gotten an error code doing a backup of Windows Server 2008. I've

spent about 30 minutes trying every imaginable search of Microsoft's

site, but can't find an explanation. Any one know where I should

look?

The full message is: "Backup started at {long string of numbers}

failed as Volume Shadow Copy. Operation failed for backup volume with

the following error code: 2155348001".

I do backups daily, but only get this message occassionally.

Thanks