I assume the server is your machine? What IP address is it? Start->Run and type cmd[Enter]. Then type ipconfig and look for the entry for Ethernet to get your IP, subnet mask, and gateway. Do the same for at least one other computer.
Sorry, should have included ip addresses.
Router set to dynamic IP address assignment
Internal IPv4 is 192.168.1.130 (as it should be) on the "server" machine
subnet mask 255.255.255.0
gateway 192.168.1.1 (Router IP)
One of the laptops returned the same, except it's own IP was 192.168.1.133
It's not an internal IP address problem as far as I can see. Between other machines I was able to manually enter an IP address and establish a connection. (3 of the 5 in our group are IT/software QA/web QA types, respectively), so it shouldn't be anything that obvious (I wish it was)
And by this, I assume that the player entered your "internal" IP address and not the one exposed to the internet...
Not sure if I missed it, but did you have someone try to connect from outside your lan during testing?
Not in our last iteration with this MT build, but we've been able to do it in the past. I expect it would work. Will try tonight if possible.
re: UPnP vs Port Forward - One or the other, you pick but you can only use one or stuff breaks.
I've tried all 4 combinations of on/on, on/off, off/on, off/off (for the sake of completeness), and none seems to work. I've used port forwarding before for Teamspeak, running game servers, etc... so I'm fairly confident I'm doing that part right.
Another possibility is that your server's firewall is indeed NOT off. This is a common problem with Anti-Virus software as they think they are smarter than the normal user(well.. they usually are!) and make it REALLY hard to REALLY turn it off. I don't know specifically about AVG, but Norton is a big PITA...
The only firewalls installed on most of these machines is the one that comes bundled as part of Windows XP or Win 7. I'm fairly certain I know how to turn those completely off. AVG Free is antivirus, but no firewall.
Can the server connect to itself via a second instance of MT, both from the lan tab and direct connect using it's internal IP(if that does not work, also try 127.0.0.1)
The server machine can host multiple instances of MT running at the same time, and yes, they can connect to each other.