I am trying to set up my XBOX 360 as a Windows Media Center Extender. I input the code as shown on the XBOX screen, but I get the error message: "Cannot Set Up Extender."

This means that the Extender was found (there's a separate error msg for extender not found), however it can't be set up. Windows points me to this page which tells me to change my router settings to enable multicast and UPnP. My router doesn't have those specific settings but I did open all ports for the XBOX.

What is odd about this problem is that it did work, then I restarted my computer and didn't change any settings, and now it doesn't work. I guess something did change, but I can't figure out anything else to try after opening all ports. I'm running Windows 7 and the router is fairly recent (I bought it about six months ago) so it should be able to handle this. The router firmware is up to date.