Delete all instances of sephwid.xml on file system. Possible locations (usually only in the PersistedData folder):
C:\Program Files\Common Files\Symantec Shared\HWID\     (if it is migrated from 11.x);
C:\Documents and Settings\All Users\Application Data\Symantec\Symantec Endpoint Protection\PersistedData\
  (Replace "Documents and Settings\All Users\Application Data" with "ProgramData" on Vista/Win7/2008+)
C:\Windows\Temp\
C:\Documents and Settings\<userName>\Local Settings\Temp\
C:\Users\<userName>\AppData\Local\Temp\     (on Vista/Win7/2008+)
  
Remove all copies of communicator.dat from the file system. Possible locations:
C:\Windows\Temp\
C:\Documents and Settings\<userName>\Local Settings\Temp\communicator.dat
C:\Users\<userName>\AppData\Local\Temp     (on Vista/Win7/2008+)
  
Delete HKEY_LOCAL_MACHINE\SOFTWARE\Symantec\Symantec Endpoint Protection\SMC\SYLINK\SyLink\HardwareID
  
Delete HKEY_LOCAL_MACHINE\SOFTWARE\Symantec\Symantec Endpoint Protection\SMC\SYLINK\SyLink\HostGUID