Group Policy Remote access

We’re trying to edit a group policy remotely on a p/c on our network but it fails because we either have “no appropriate rights” details “no network path not found” (it pings ok and is seen on the network). We were able to do it a couple of months ago but now cannot. XP sp2 is applied, ports opened and firewall disabled, we tried it from a non sp2 system with the same results. We can mmc a computer management snap-in but not group policy object editor snap-in. Any ideas?