Hyper-V vss writer failed [7] timed out

Hi

We have started to backup Hyper-V VMs, on Hyper-V on Windows 2012 R2

The backup fails and we found that the Hyper-V vss writer has failed with status [7] timed out on the two hosts owning the VMs we are trying to backup

Unfortunately we are not allowed to restart the Hyper-V Virtual Machine Management service which should reset the Hyper-V vss writer

Have found nothing the system & application eventlog, which have made me wonder if it is a shadow area issue.

Regards

Michael