[问题求助] no NAT in vpn help

setup a VPN on a netscreen 25. I was able to connect to it with a laptop doing dialup. I was able to ping and see the server im connected to. I was able to map a drive etc.. and browse the files. Now i try the samething on a cable internet line. I was able to connect but now i can ping the server that im connected to. I then look in the logs on the netscreen 25 the only thing i see different for these two types of connection is that with the cable internet i get this line "Phase 1: IKE responder has detected NAT in front of the remote " eDDFRpg:!U  
So how do i go about enabling the NAT? any help would be great!