Cobra: I have a possible idea as to why you are getting dropped connections. I remember that you were previously able to play without problems -- have you recently turned on "Improve UDP/IP Networking Quality" in Configure --> Miscellaneous? If so, turn it off, and see if you still have connection problems.
I remember turning this on one day, and then the very next time I tried to play a netgame I would experience the same issues as you did -- I would get dropped after 5 or 10 minutes of play. Once I turned this option back off, everything returned to normal.