I do know your model of router is one a bit of a lemon. Linksys normally release great devices but unfortunately those ones apparently have firmware problems which results in them being unreliable (particularly in UPnP mode.) My recommendation would be to forward a port. Find your model here http://portforward.com/routers.htm

There's been a few people who have reformatted & reinstalled their windows media centre & then had problems reconnecting with any p2p program.