I seem to have found a bug. It is something that has been an immense pain in the butt for quite a while. But we did not know what caused it.
Basically whenever we rendered a sequence, the file would crash. It would render the first frame and maybe the second frame, but then crash when the next frame starts to render.
I have tracked it down to the source which seems to be railclone, more specifically when railclone is being projected onto a surface.
We build our terrains lately using this technique, because it allows us to make changes to the road or terrain very quickly.
If I put a edit poly modifier on top of the railclone object, the crashes disappear, but this defeats the purpose of using railclone to save up on memory.
I can supply an example if you would like.
I am using Railclone 2.5.0 and Vray 3.3