Sounds like an issue with your network card and/or drivers. To be sure, does the problem only occur when you're actually RUNNING torrents? What kind of network card are you using? How many torrents are you running at a time? uTorrent, generally speaking, is one of the best BT clients out there in terms of stability, so it's probably not the program itself, but how your computer handles it. I've had similar issues with bt clients before, but in order to help you, I'll need more info.