OK, so the client sent 1st message and is waiting for the 2nd message from SSG.
SSG has sent 2nd message and waiting for 3rd message from client.
Is it possible to go for Wireshark capture on the client to confirm it is not receiving the 2nd message from SSG?
If it's indeed not receiving the packet, it might be worth looking at the NAT device in between (the one NAT-ing client from 192.x to 46.x IP)