Video Coding

I have some video that has the mpeg 4 quicktime logo but will not play in quicktime at all. However with vlc they play great. In the information window (in VLC), i checked the coding of a video i have that play fine in front row and quicktime, against one of the ones that won't. They both say avc1 for audio and mp4a for video. Also visual hub will not convert the files to mp4, something about missing a audio codec or something. Any ideass would be great

Thanks
Eric