Right guys if you're still having this problem I can think of 1 thing you can try.
Because, (and I'm assuming that) you are running behind NAT and forwarding ports,
it may work with some routers but not others. Some routers have UPnP which may solve the issue.
What I suggest you try is log into your router and enable DMZ (de-militarized zone)
point it to your servers internal IP.
On that server, enable the firewall and make sure you go over the rules so it's secure, since any non-return traffic will now be forwarded to it.
Set up a firewall rule specifying the DCS executable, not port numbers, and allow traffic.
We run a server on a static public IP so don't have these issues.
Come to think of it if your router is using a dynamic IP, that IP may change while the server is running, and that would cause it to come off the list, so a static IP is pretty much a must or you will have to restart the server every time it changes.
If your router does not have a DMZ or similar setting or you don't have access to your router well then you're out of luck.
