Solution: Config Error when conne Xbox360 to Media Center Vista

I hope this works for you as it did me:
I was getting the -.209 error when trying to connect my Xbox360 to Media
Center Vista Ultimate. After trying several of the online recommended
Microsoft solutions these two url's led me down the path that solved my
problem; http://forums.xbox.com/11496426/PrintPost.aspx, and
http://technet2.microsoft.com/window....mspx?mfr=true.

After reading the entire posts you will find that it recommended pouring
through log after log of your event viewer. After spending several hours
doing this I found that Event ID 405 was my problem. Following the link to
research the even further led me to the -.209 error code which had six
possible solutions. I decided to try the most obvious first since I had the
device enumerator error listed in the viewer which was linked to a security
violation under another event id. I connected the xbox to the PC directly
which worked! So I concluded my problem was the router configuration. I
factory defaulted my router and compared the settings to the overwritten
settings and found that the only difference other than firewall and password
of course was the router by default set UPnP "disabled" and Multicast pass
thru "disabled". The router Linksys WRT54Gx2 was recently upgraded to latest
firmware 1.0.22 from Linksys during the troubleshooting process and I
discovered the old firmware version 1.0.9 of the firmware had set these two
setting "enabled"on by default. I then re-enabled these two settings and the
XBOX dropped connection almost immediately.

More investigation and playing confirmed the Multicast setting is causing my
grief.

Reading the forums it is recommended that multicast filter be enabled, not
clicking for a long time the multicast settings in my router are to enable
the opposite than expected outcome. What I mean is pay attention to the
wording of the text strings where you enable or disable the setting. On three
differnt routers the wording was differnt for all three on Linksys routers.
One was labled "Multicast Filtering" in which you would want to have this
enabled; while the router I'm using now is labled "Mulitcast Pass Thru" in
which the correct setting is "disabled.

Hope this helps.