VSS Post Backup failures for Virtual Server 2005 R2 SP1 virtual machines

We've been seeing strange errors with Volume Shadow Copy services on our Virtual Server 2005 R2 SP1 host. It appears to be failing on a strange mountpoint in the C:\WINDOWS\Temp\ folders, which I believe is used by VSS to mount a writeable image file.

To summarize:

1. The Microsoft Virtual Server 2005 Writer continually goes into a failed retryable state
2. The Virtual Server log reports errors during the Post Backup phase
3. VSS reports errors backing up a mount point of unknown origins
4. The mount point causes NTFS and ftdisk errors

The host is x86 Windows Server 2003 Standard, SP2. The virtual machine is the same. Both use basic disks.

Here is the writer state:

Writer name: 'Microsoft Virtual Server 2005 Writer'
   Writer Id: {76afb926-87ad-4a20-a50f-cdc69412ddfc}
   Writer Instance Id: {78df98e2-bf19-4804-890b-15865efef3bd}
   State: [11] Failed
   Last error: Retryable error

From the Virtual Server log:

Virtual Server - Vss Writer - Event ID: 1035:
The VSS writer for Virtual Server failed during the PostBackup phase. 
The guest shadow copies did not get exposed on the host machine, 
after mounting all the virtual hard disks of the virtual machine VMACHINE.

From the Application log:

VSS - None - Event ID: 12290:
Volume Shadow Copy Service warning: GetVolumeInformationW(
\\?\Volume{fb84bae7-87f5-11dd-9832-001cc4961ca6}\,NULL,0,
NULL,NULL,[0x00000000], , 260) == 0x0000045d.  hr = 0x00000000.

From the System log:

Ntfs - Disk - Event ID: 55:
The file system structure on the disk is corrupt and unusable. 
Please run the chkdsk utility on the volume C:\WINDOWS\Temp\
{fb84bae7-87f5-11dd-9832-001cc49....

My current theory is that VSS creates a mount point for an image file of the VHD, then the software panics for some reason, leaving everything in an inconsistent state. Removing the mount point doesn't resolve the problem. All of the other disks check out fine with CHKDSK. There's no exclusion option for VHDs or to turn off online backups.

Has anyone seen this kind of thing before or point me in the right direction for getting more information about the mount point and it's origins? I haven't been able to trace what application is creating that mount point.

This is Tom

I am assuming from the error and the research I have done that you are running this as an online backup, this usually only affects online backups with dynamic drives, but.

For experimental purposes, i.e. As a test, have you tried changing this to an offline backup to see if you get the same results.

If it works then either leave it as an offline backup, or I'd recommend calling the Microsoft VS 2005 team for support