I get 1 or at most 2 turns into a multiplayer game of HOMM5 with my brother and someone gets disconnected. Any reasons?
I have all the ports forwarded, and we have no issue connecting to each others games.
Are you 2 in the same house on the same network? Sometimes it has to do with the router itself.
See if you can find any firmware updates for your router/modem from the manufacturer's site.