Mostly every torrent downloader requires to connect to more peers and seeds so it makes changes to windows tcpip config file to more than the maximum number of connections allowed ... some of the possibilities would be ... and i mentioned how to make your Internet stable ..
You have limited your upload speed ?
Install your old version of Azureus and test again. If the problem goes away either update to Azureus CVS (simply replace azuerus2.jar) and retest.
A colleague guessed that maybe Azureus was causing my router to crash?
Quite likely. If the above doesn't fix the issue, try each step below, restart the client and test after each step.
1) Open the UpNP tab and see what the messages are
2) Disable uPnP at client
3) Ensure DHT UDP port is forwarded to the client, not just open the port but forward also.
4) Disable DHT at client (DHT overwhelms some routers with connections)
4) Set your network adaptor and IP in Advnaced Network settings and specify ports