"The key here is to look at the configuration
on the VPN concentrator. You need to setup
NAT-T on the VPN concentrator, as follow:
Configuration | Tunneling and Security | IPSec | NAT Transparency
There is a check box for "IPSec over NAT-T".
Check that box and it will work.
"
Thats correct. I understood just the opposite at my first fast look at the question, thats why I rejected to not to NAT-T at PIX side.
"Cisco VPN client does not use PPTP protocol"
Thats correct too, but I didnt see any statement about Cisco VPN client, thats why I suggested it. But if I recall correct, client shouldnt have been able to establish connection if it was a PPTP client, without the fixup protocol I mention. So most probably it is Cisco VPN client.
Setting NAT-T at concentrator will resolve the issue as you mentioned.
Brian, if still no joy after setting NAT-T in concentrator, we need the config of concentrator.
