Ok, I have investigated and it is actually the windows defender advance settings. I assume Bullguard inherits these, so when the firewall is turned off the rules aren't applied.
The the thing is it was working ok as I hadn't changed anything. Also to add I always run with admin rights.
Jason (and anyone else who runs into a similar issue)- This is what you need to do.
If you go into Bullguard Manage Rules and then in the bottom left click View advanced Windows rules, it take you to the Windows Defender setting page.
From here select Inbound rules on left hand side
Then look for Aivlasoft 2,
here you can see the local port is set to 13. You then need to select it and click properties on the right hand side. You then get a pop up window and you want to select 'Protocols and Ports'. You than want to change the local port from 13 to 51748 and hit apply. Alternatively you can also change the drop down box to 'All Ports' and that works as well.
Now when you run the server it will open error free.
As I said , up until recently it has always worked ok and the setting was port 13, so no idea what has changed.
No, I was just referring to recent cumulative update, (perhaps not significant)