Phones not ringing

[acrumpton]

We are running V6 on a dedicated server.
All our phones are remote (over the Internet).
The 3Cx server is on a broadband connection in bridge mode. All ports go to server.

I am using Snom 320, Snom 360 and X-lite in different locations round the Country
Have also tried 3Cx client.

The Snom360 is able to make and receive calls
The others do not receive calls

Here is an extract from the log between the 2 failing phones
For security I have replaced the IP addresses with IP_address_1 and IP_Address_2

14:36:13.955 Call::Terminate [CM503008]: Call(5): Call is terminated
14:36:13.939 Call::RouteFailed [CM503015]: Call(5): Attempt to reach [sip:302@IP_address_1;user=phone] failed. Reason: Server Failure
14:36:13.939 CallLeg:nFailure [CM503003]: Call(5): Call to sip:302@IP_Address_1 has failed; Cause: 503 Service Unavailable; warning: ; internal
14:36:13.814 CallLeg:nFailure [CM503003]: Call(5): Call to sip:302@IP_address_1:5060 has failed; Cause: 503 Service Unavailable; warning: ; internal
14:36:11.365 CallCtrl:nSelectRouteReq [CM503004]: Call(5): Calling: Shared:Ext.302@[Dev:sip:[email protected]:59495, Dev:sip:302@IP_Address_2:59509;rinstance=9a115276019b696e]
14:36:11.365 CallCtrl:nSelectRouteReq [CM503010]: Making route(s) to [sip:302@IP_address_1;user=phone]
14:36:11.365 Extension:rintEndpointInfo [CM505001]: Ext.301: Device info: Device Identified: [Man: Snom;Mod: 320;Rev: General] Capabilities:[reinvite, replaces, able-no-sdp, recvonly] UserAgent: [snom320/7.3.7] Transport: [sip:IP_address_1:5060]
14:36:11.365 CallCtrl:nIncomingCall [CM503001]: Call(5): Incoming call from Ext.301 to [sip:302@IP_address_1;user=phone]

Any ideas gratefully received

thanks

Andy