Unable to register with pbxes.org

[occamsrazor]

I've set up my Obi110, and have it registering with Gizmo5 ITSP no problem.
However I'm unable to successfully register with the virtual pbx provider www.pbxes.org
Settings used are:

Service Provider Proxy Server: pbxes.org
Service Provider Proxy Server Port: 5060
Outbound Proxy Server: <blank>
Outbound Proxy Server Port: 5060
User Name: <username>-<pbxes extension> e.g. joebloggs-200
Password: xxxxx
Port 5060 is forwarded to the Obihai device.

I've been using SPA-3102 devices for a long time, and have the above details used in my Linksys working fine.

But on the Obihai all I get is "Register Failed: No Response From Server"
As I said, the registration with Gizmo5 ITSP works fine.
I've also tried calling the Obi110 from my Obion on my iPhone and that works fine too.

Any ideas?

[OBiSupport]

Our next firmware release will have the fix for this.

Sincerely,
-Obihai Support Team