Your ISP might be throttling p2p.
broadband help » Forums » Fiber Optic » MstarMetro throttling p2p connections

What speed did you get when you downloaded a magnetmix file? Slow speeds there can be a pointer to an ISP throttling.

Try changing ports. Use something between 49152-65535 (a few people use 64049). You can change FW's listening port via tools > options > advanced > firewall config. Any ports forwarded within a router will have to change as well