Windows 7: WMC Extender For 360 - Issues playing Videos...

Alright,

I have an XBOX 360 Elite. I've updated it to the latest version.

I'm now having problems playing Videos. Some work, some don't. The ones that work, play flawlessly, but the ones that don't work play for a few seconds, then stop and say this video can't be played because of codecs, the weird part is, I can watch that same video on my computer, and my brother doesn't have issues on his 360.

I mostly play AVI, MP4, and MKV. The MP4 and MKV use the h.264 Video codec, and the audio is in Nero-AAC codec.

Can anyone explain to me why this is happening, and possibly give me a fix for it? Its driving my mom batty, and driving me insane because I have to put up with her.