vssadmin issues with windows server 2012 R2 clustering

Hi I have a three windows 2012 R2 servers with windows clustering installed and set up as a SQL availability group.

When I try a backup (Backup exec 2014) it fails with VMware error "An error occurred while quiescing the virtual machine". When I run vssadm list writers I see "These may be delayed if a shadow copy is being prepared".

These are cluster errors in the event log for "The cluster Resource Hosting Subsystem (RHS) process was terminated and will be restarted"

Now if I stop the cluster service and try a backup it completes and vssadmin list writers returns the expected results.

I want to run the backup without having to stop the cluster service.

Thanks