OK you are doing everything correctly. Does the P4 box have HT enabled? Try playing with that one if it does/doesn’t. Check if the P4 box has the windows firewall enabled and disable it. Check also the opteron machine for firewalls. Do you have any antivirus on both machines running? If any of these don’t work, re-install VRay on both machines and try again. If again the problem persists, the last thing I would do is to uninstall SP2 on the P4 box. Ah, is your max70 installed (and not copied) to both boxes?