Can no longer backup VMs using DPM 2012.

Hi,

   Up until Fri last week all our backups have been working well. Then all of a sudden both Hyper-V servers in a cluster no longer backup VMs. The error we get is:

The VSS application writer or the VSS provider is in a bad state. Either it was already in a bad state or it entered a bad state during the current operation. (ID 30111 Details: VssError:A function call was made when the object was in an incorrect state
for that function
 (0x80042301))

Nothing has changed on the servers and we can only do backups of servers that have agents installed in them, ie. SQLSERVER and EXCHANGE. But VM backups using the Hyper-V Writer always fail?

Can anyone help please?

Regards

Simon