As I had indicated yesterday, in Word 2007 there is a fatal flaw, see This. The flaw is as follows.
Suppose you want to create an index.
Suppose you want to index the following:
brown
horse
brown horse
Now you can get an index in an index. What then apparently happens if that you can get the storing of the docx file in a manner where you loose one of the xml commands and when you try to reopen it, gone! All of your work is un-openable.
You may try to recover via the suggestions linked above but by looking at the above you find that at first they had no idea what the problem was.
I have gone through all my books and cleaned the xml index commands and Index entries. Hopefully that works.
Could you imagine if Toyota made a car that randomly blew up, or a heart valve that randomly jammed, and the maker was aware of it and did nothing! This is the worst case of a bad and dangerous product I have even seen.