When the Symantec Management Agent is installed and allowed to start, it generates a GUID. The updated Citrix image then heads out with a duplicate GUID. To avoid this problem, after installing the agent, stop the service, delete that GUID from the database, run /resetGuid, delete references to the machineGuid in the registry, then take your image. When the image is deployed, I assume this involves a computer restart, at which point the Symantec Management Agent automatically starts, finds that it has no GUID, and then creates one and notifies the Notification Server. This should ensure everyone has a unique GUID.