I've got a problem with an animation.

I have a box that jumps a couple of times from right to left. stops, turns around and jumps in a different direction.

In the playblast, this comes out all fine and dandy. But when I render it, it comes out different. The box jumps how it should, but when it lands for the final time, ready to turn around, in one frame the box shifts position.

I'm using trax and keyframe animation for the box. But I can't see anything wrong in the graph/trax editor.

To show you what I'm going on about, I've put it online here . It's about a meg big.
Look at around 7/8 seconds and 25 seconds to see what i'm on about.

Help! Please!