I just got my new PC a few days ago and the ONLY thing that didn't run absolutely flawlessly was AOM when I tried to connect to anyone through gameranger. Since this is one of my most favorite activities I was going crazy trying to figure it out. I even went so far as to re-image the PC. Still, it would not work.
The symptom I was having was as follows: I could connect to gameranger fine. I could connect to a friend using the the direct connect feature. But when I launched the game as the host, anyone I was trying to play with would remain at the LAN/Direct IP screen and after 15 seconds they would time out. I tried having them host and then it would be me sitting at that screen for 15 seconds and timing out. I updated every driver and examined every setting in on my modem/router. No Luck. I literally worked on this single problem from 7 pm until 4 am. Still no luck. It worked fine on my old PC so what's the deal? I even hooked up the old PC again just to test it. Very annoying.
The ONLY thing I could think of that might cause a connection issue at this point was the NIC. Sure enough, my motherboard has a built in Bigfoot Killer 2100 NIC and that was the issue. I can't tell you why it was happening, only that when I went and bought a USB NIC and plugged it in, perfection. The crazy thing was, both AOM and Gameranger worked flawlessly by themselves but as soon as they tried to work together, stoppage.
This is probably one of the most frustrating issues I've ever faced with a game so I thought I would try and save anyone else that might be having this issue the grief that I had. I'm a technical lead for a gigantic pharmaceutical company so this turned into a personal challenge for me. Good luck all!