megui question

After viewing 17 seconds of my render i recieve this msg at top of screen:
AVIStreamSynth: System exception - Access Violation at 0x0, reading from 0x0

It's not after the sony vegas render, but after the render with megui.

My avisynth script:
AVISource("test1234.avi")
Crop(0,0,-0,-0)
ConvertToYV12()

Tried googling, and haven't got activasion on Doom9 yet. Any suggestions?

EDIT:
The render before I used the muxer to combine the audio with the movie.