Nortel client behind PIX with PAT second time

Hi,

I have Nortel client V04_65.30 behind the PIX 515E V6.3 (4) configured with PAT (Only one public IP address available) dialing in to Nortel VPN server. Nortel client, server and PIX are NAT-T enabled. PIX is VPN enabled (isakmp) for dial in using Cisco VPN client for mobile users. When I try do dial out using Nortel client behind the PIX I get error message "server not responding". If I disable isakmp outside and enable "fixup protocol esp-ike" Nortel client works, but it is not solution as a I have hundreds of client who need dial in. I see that Nortel client initiate connection on UDP port

John