New to me this morning is this error:
The server fault 'SystemError' had no message. Error Stack: Call "PropertyCollector.RetrieveContents" for object "propertyCollector" on vCenter "vCenterNAME" failed.
This happened to all my templates after converting them to VMs and trying to edit settings.
Hmmm... I hadn't changed anything since upgrading to 4.1u1. Maybe that caused the problem, maybe it was something else.
The fix: unregister and re-register the VM. Done.