Checked protocol rules -> same as before with no apparently problem. ISA server is not on a domain controller it is an independent machine. I tried even with a allow all protocol to any request rule and nothing. All computers are on the same subnet. Checked the LAT -> OK. DHCP has plenty addresses to give. Ping to outside allowed. Could it be a problem the fact that we have a supernet DHCP 192.168.1.x - 192.168.3.x (shouldn't be - the ISA and most of the computers with problems were in 192.168.2.x)