OK, this is resolved now.

I was having issues with getting the A/S service to connect to FDN. Turns out that the firewall was doing deep packet inspection of outbound traffic and the default port 53 that it uses to communicate over is allowed out BUT the packets don' t look anything like a DNS request so were rejected. That' s why I could ping but not connect.
I tried changing to 8888 and 8889 but still no luck. Eventually, I ran Diag Sniffer Packet on the interface that FML was connected to and just captured traffic going to FDN. I could see the port 53 traffic coming into the firewall but no corresponging replies. So, with the filter still on I changed it to talk over 8888 and 8889 but the traffic remained on port 53. I stopped the service to check that I was looking at the right traffic and sure enough it stopped. When started the service again it changed to 8888 and away it went working perfectly.
The answer is that the ' Apply' button doesn' t work as it ought to, it saves the changes but doesn' t apply them. I guess a change then reboot would work but just stopping and restarting the service does the trick.