Windows Server Backup Fails On Scheduled Task

Hi

We have a 64bit 2008 Std Server (SP2) running a scheduled backup to a virtual hdd, the backup is just over 60gb.

Recently the backup fails with two messages

C: System cannot find the path specified
Other Drives: The backup of the volume was stopped before the backup started running

If the backup runs on the schedule then it will only backup 1.63gb of data on drive C: then stop.
However, if we run a onetime backup using the same configuration as the schedule then the backup will complete perfectly.

We have recreated eth backup job but still receive the same results all round.

We are currently receiving the following error in the logs:


EVENT: 517

<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
- <System>
<Provider Name="Microsoft-Windows-Backup" Guid="{1db28f2e-8f80-4027-8c5a-a11f7f10f62d}" />
<EventID>517</EventID>
<Version>0</Version>
<Level>2</Level>
<Task>0</Task>
<Opcode>0</Opcode>
<Keywords>0x8000000000000000</Keywords>
<TimeCreated SystemTime="2012-08-13T13:53:46.262Z" />
<EventRecordID>2043496</EventRecordID>
<Correlation />
<Execution ProcessID="8080" ThreadID="8196" />
<Channel>Application</Channel>
<Computer>RESCUE.autorescue.local</Computer>
<Security UserID="S-1-5-18" />
</System>
- <EventData>
<Data Name="BackupTime">2012-08-13T13:17:43.830Z</Data>
<Data Name="ErrorCode">2147942402</Data>
<Data Name="ErrorMessage">%%2147942402</Data>
</EventData>
</Event>


Any help would be greatly appreciated.