An error occurred while taking a snapshot: Failed to quiesce the virtual machine

I am trying to clone a virtual machine but the task fails with the following error:

An error occurred while taking a snapshot: Failed to quiesce the virtual machine

I also see Event ID 7011 logged in the System event log on the VM in question:

A timeout (30000 milliseconds) was reached while waiting for a transaction response from the VMTools service.

I have checked the VSS Writers, restarted the VMware Tools  service and even restarted the VM, but it still fails.

I resorted to attempting a clone with the VM powered down and this was successful.  I suspect it may be down to licensing (as the host only has a Standard license, not an Enterprise license) but will research this further.