I have a server on one of the several PCs in my home. When I run it, my friends can connect just fine. If someone in my house hold gets on on the other hand, they are on for at most 3 minutes before they get kicked and then no matter what PC or Laptop you try to use we can't get back on unless the whole server gets rebooted. In the mean time all of our friends are untouched. It is just anyone trying to get on at home that is having the issue
The error that shows up on my laptop and any other home pc are:
External ip - "Connection refused: No further information"
Internal ip - "Authentication servers are down. Please try again later, sorry!"
On the actual server list it then shows "Can't connect to server"
That's really strange. Definitely some kind of weird networking going on. You shouldn't have any problem connecting using the external IP if everyone else isn't have problems. But that said this is hard to diagnose without a better understanding of your network.
It's possible but unlikely it has something to do with your port forwarding. I would look into your firewall rules on the server, and your router, (maybe even turn debugging/logging on and see if you can find a deny entry). You also might be able to find a duct tape solution using NAT translations or maybe try and put the server into a network DMZ.
Sorry for being vague and probably not very helpful but there's not much I can suggest without knowing more about the network/routing.