Following an upgrade to vSphere 4.1 I was unable to edit the settings of a template which had been converted to a virtual machine; with the following System Error:
Call “PropertyCollector.RetrieveContents” for object “propertyCollector” on vCenter Server “vCenter Server FQDN” failed.
To resolve this issue you are required to shutdown the virtual machine, remove the virtual machine from the inventory (make a note of the datastore location) and re-add the virtual machine by browsing to the virtual machine folder from the datastore and selecting the .vmx file to add the virtual machine into the inventory.
Deans Blog 