Webcam won't connect and files won't transfer

I am unable to view my contacts webcam and they are unable to view mine. We
get each other's invitations but it won't connect when we accept the
invitation. I can see my own video in the video window so I know the webcam
is working fine. After a little while, it comes back with an error "unable
to connect". Also, single file transfers are either extrmely slow, or won't
happen at all. I am connected through a linksys router. I've opened up ports
6891-6900 as well as enabled UPnP. I've shut down zone alarm. I've
uninstalled Windows Live Messenger and downgraded to MSN Messenger 7.5 but
nothing seems to work. Funny thing is that my laptop that's on the same
network seems to be working just fine.