I have had this problem exporting to pdf because of file size. Have you tried exporting it in 100 page increments, or something like that?
I would export it as a PDF file and save it by 100 each out of the 400. You probably have a large file size and its probably making InDesign be overwhelmed with the amount of pages that you have. If that does not work, try to break the file down in half by creating a new file and copy then paste only half of the documents that you have and see what happens. Try a little at a time.