Network not working when Norton IS 2011 is installed

I have a home network setup which includes a Windows 7 system and a Windows XP system. Also in the network is a network printer. The Windows 7 system prints fine but does not see the XP system. The XP system does not print and does not see the Windows 7 system.

 

If I remove Norton IS from the XP system all is well, the printer springs into life and the networks on both machines see each other. What is the reason for this?

 

Windows Firewall is off and I have even exited totally from Norton IS on the XP machine but the only solution seems to be to remove it totally.