I am having a problem with shared folders. I opened a folder up with a friend and found out that it wont snyc (Sharing folders can't snyc right now but will try again later). Here are the things i have done, I have disabled windows firewall, i have no 3rd parts security software, and it still dosent work. I am behind a router (Linksys BEFW11S4) with pretty much default settings WITH UPnP ENABLED. I have tried everything from forwarding the entire range of possible ports to myself to setting myself as the DMZ all with no luck. Directly connecting my computer to my modem though does allow my shared folders to work ! So the problem is definately the router, any help with settings or ideas on this one?

Other stuff: Windows XP Pro Sp2 Fully Updated
Router Firmware (1.50.02) - most recent i think

I also removed all security settings on the router to try and make it more transparent all with no success.