The following error may be displayed when attempting to enumerate a WSUS Computer Group in the EminentWare console.
Source: Data Grid Server (xxxxx)
Exception occurred at MM/DD/YYYY 0:00:00 PM: Unable to retrieve the computer group by ID for enumeration. Group ID: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxx
Refresh the Update Services node
I found the answer:
Go to the Update Services Node and select refresh twice.