SharePoint Foundation: Error when performing a Farm Backup

Hi,

I am trying to create a full farm backup of my organisations SharePoint Foundations installation.

I've tried doing it via the Central Administration and PowerShell. However both ways give me errors. Here are some of the errors associated with the Central Administration way of doing a full backup:

Requested By  Domain\Administrator 
Start Time  1/10/2012 2:49 PM 
Finish Time  1/10/2012 3:06 PM 
Directory  D:\SharePoint\Backup\Test Back ups\spbr0000\ 
Backup ID  553b4f4f-7542-4e80-b129-d3d294285486 
Warning Count  72 
Error Count  16 
Failure Message  Object Query-0 (C: on SharePoint Server) failed in event OnBackupComplete. For more information, see the spbackup.log or sprestore.log file located in the backup directory.  

I've also got error reason 15105 coming up a lot too.

Can anyone please tell me how I overcome this problem please.

Regards

Stephen