Why are MP4s that Vegas renders invalid in QuickTime?

Hello! I'm wondering about a strange problem that's dogged me in Sony Vegas 6, 7, and 8. I've tried rendering to both "MainConcept AVC/AAC" and "Sony AVC" and and trying many finer options within, but the resulting MP4 plays fine in QuickTime Player with a few quirks which leads me to believe it's less than fully-compatible:

* The first frame always shows as black.
* Checking the properties (via Window menu > Show Movie Properties) shows "Data Size" to always be "-NA-".
* Trying to export the video from QuickTIme into other formats results in this error:

"Error -2015: the movie contains an incorrect time value"

I really like the quality of MainConcept AVC/AAC, and I'm hesitant to render to "QuickTime 7" because H.264 isn't available ("H.263" is but that's worse, and "MPEG-4 Video" is different, right?) and furthermore, there are no really good audio formats: I can't use MP3 or AAC, and would likely end up having to render again (with video passed through) in QuickTime.

Does anyone know how to work around this, or a better way of generating fully QuickTime-compatible files? I'd like to encode some high-quality videos which are web-streamable, but it looks like the only convincing way to do that without suffering noticeable quality losses is via QuickTime Player itself, which I can't do straight from Vegas.

Any help is enthusiastically appreciated, thank-you in advance :)