User cloned couple of computers from win XP to Win 7 ,After cloning those computer the GUID ID of thoes computers remains the same,So because of that there are couple of issues arises.The basic thing to do if there is a GUID issue is to download RAAD tool and try reset the GUID ID thats should resolve the issue. else go through the below article which will explains about the dupication of GUID and the issue which might be created because of it and also gets reports of all the shared GUID and how to reset agents
http://www.symantec.com/docs/TECH142625 Shared Guid Toolkit
http://www.symantec.com/docs/HOWTO21449 RAAD tool download link.
http://www.symantec.com/docs/TECH133462 Effects of duplicate guid