can you render a single frame?  it might not be the animation but something not coming up for the first frame
shadowcasting can cause memory errors and drop the frame on a single frame, or textures not native to the runtime you're using.
it is true that rendering an avi is harder than frame sequence.  better to render the sequence in frames and glue together elements in an avi editor.

go that way really fast.
if something gets in your way
turn