Hyper-V VSS Writer error

Hi,

In the last few days or so we have been experiencing failed backups. The backup fails at 'Check VSS snapshot and consistency' in BackupAssist 7.4.5 software. Below is the error message:

The backup operation stopped before completing.
Detailed error: ERROR - A Volume Shadow Copy Service operation error has occurred: (0x80042336)
The writer experienced a partial failure. Check the component level error state for more information.
A Volume Shadow Copy Service operation failed. Please check "VSS" and "SPP" application event logs for more information.
ERROR - A Volume Shadow Copy Service operation error has occurred: (0x80042336)
The writer experienced a partial failure. Check the component level error state for more information.

We are running a HYPER-V 2008 R2 Server with two virtual machines - SBS 2011 Standard and Server 2008 R2.

I ran 'VSSADMIN list writer' in a command window on the host machine (HYPER-V Server 2008 R2) and there was an error:

Writer name: 'Microsoft Hyper-V VSS Writer'
Writer Id: {66841cd4-6ded-4f4b-8f17-fd23f8ddc3de}
Writer Instance Id: {3cd8204b-5f3a-4e5b-b7e8-b605c26ad538}
State: [5] Waiting for completion
Last error: Unexpected error

Using Windows Backup on the Hyper-V server also generates the same error message.

We would be grateful for any advice.

Regards,
Mark