Half renders when rendering a animation?


I have started rendering some part of my animation an have some render issues. About of a 10th of the frames only render the botom half?
When I render it as a individual frame there fine but as a animation it keeps poping up?

When rendered as a animation!

When rendered as a single render?

Im exporting as JPEG.

Any help would be really usefull as I have a deadline in about a week an have about 2 mins to render and carnt afford to rerender the frames individualy!

Also Just using blender internal!