After creating a snapshot of an Encryption Management Server that runs as a guest machine in a VMWare environment, it stops responding. It is still possible to ping the server, but the services are not available.
In the vSphere interface, one can see:
An error occurred while taking a snapshot. Failed to quiesce the virtual machine.
This is a known issue affecting vSphere ESXi 5.1, 5.5, and 6.0.