This sure sounds like the IGMP proxy problem. If you have a 802.11n router (rev I), the IGMP proxy settings are hidden. If you didn't find the magic URL to un-hide the settings, you may not have actually turned IGMP off. Here's the magic:
You need to be logged into your router for this to work.
If you have indeed turned off IGMP proxy, I'm at a loss.
Good Luck