Have you taken any drugs at some point working on your project?
Heheh, seriouslly, never seen this in either 5 or 6, have you tried render another file and see if the same thing occur, maybe the file got corrupted at some point!
I'm using ASd 6 is why I render at 2999 frames. I render at 100 and at 500 and it comes out fine, it's only when I render the whole 2999 at one time does it do this.
Until i find a way to keep the audio if i render it in sections im screwed. If i render 1-500 it comes out great, but when i render 500-1000 i lose audio.
I have seen something very similar to this before - it happens when rendering a large video file and you consume all the available computer resources. ASP doesn't flush its memory on completing a frame render.
Try rendering the movie in batches of png and see if the same thing happens at 2999. In my case rendering in png batches of 100 fixed the problem.