Well.. a bit more info..

I fired up Wireshark and captured the register request from my PC to the SV8100:

https://www.duncanmargetts.com/blog/wp-content/uploads/2009/01/registerrequest.pcap

I also have a debug log from X-Lite showing the failed register request:

https://www.duncanmargetts.com/blog/wp-content/uploads/2009/01/x-litelog.txt

It would seem that SIP is definitely running, that I have the right IP address and Port.. but its just not happy with my Register Request frown

I have another SV8100 box here.. I'll set that up and try it.

With thanks for any input,

Dunc.