This is a old problem but we have the same problem. Our express Talk is connected thru a VPN so we have 2 IPs on the computer a "public" and a "private"(with the VPN) one.
For any reason, when the Express talk want to be registed, Express talk use the "public" ip that doesn't work. We force the private IP in the Static IP section and Express Talk never use it.
Somebody knows how to fix that?
We have to another problem where the connexion on the 5070 port failed (15% of the time it failed) ( I think it is a firewall issue) but do you know how to force Express talk to loop to another port until it get one who work? Because we change the port and the connection works.
Thanks for your time and help