Just powered down my computer, router, and modem and it works like a charm again. Don't ask me why it has less issues with a router than without, but what I do know is that my network setup is probably one of the worst possible for a P2P. In fact, Limewire is about the only P2P program that works without issue on it.

Anyways, try powering down your computer, modem, router, etc. When starting up again, go from the jack out (modem->router->pc)