Truncated animation files

I have regularly rendered animations running my pc overnight. I have one model which will only save a part of the avi file to disc. This doesn't happen with any other scenes although they are set up the same. Can anybody help please?

You should not render to avi. See my advice in this thread: http://www.cadtutor.net/forum/showthread.php?52051-Saving-only-a-part-of-animation