Update:
I recently suffered from this problem again. I was working in Word 2010 on a 40 page document with new style equations and track changes. The problem occurred sometime after I copied over an appendix that I had been preparing in a separate document into the
main one. When I went to save I got the dreaded 'Cannot save docx file - A file error has occurred' message.
Previously I managed to identify that the bug had occurred due to some issue with track changes within a modified table and was able to copy over the whole document - with the exception of the offending table. This time I hadn't made any changes to any tables
- so I knew that this wasn't the problem.
I tried the technique described above, whereby a new document with the same template is created and all contents are copied over into the new one - but once again this did not work. When attempting to save the document I still got the 'Cannot save docx file
- A file error has occurred' message - so it appeared that the track-change bug had got copied across.
I also tried saving with a different filename, but this did not work either.
I was beginning to lose hope. It appeared that the only option was to delete my 40 page document and go back to a much earlier version that worked. Before I did so I decided to look through all the track changes to see if I could spot any weirdness. By chance
I spotted that within the track changes an equation had somehow expanded to enclose some deleted paragraph text. In "Final" mode the document looked correct - but the paragraph text never was and should never have been
within the equation and I don't know how it got there. I "accepted" the deletion of the paragraph text within the equation and suddenly my document would save again.
So, in my experience this problem has always been caused by a track changes bug, either
* caused by a modification of the structure of a table - such as deleting a row or column, or
* caused by a mix up between standard paragraph text and equation text.
This is a serious bug - rendering the document completely unsaveable. Unless the user is lucky enough to be able to identify the track change bug (which can be virtually or completely impossible - especially in a large document full of track changes), the only
options open to the user are to close the document and lose all their changes or to accept all track changes.
I am a business customer and this has lost me many hours of work. When will Microsoft take this seriously and get around to fixing it?
By the way, this bug is incorrectly listed as applying to Word 2007, XP. It should be filed under "Microsoft Office Word, 2007 or newer". Perhaps a moderator, system administrator would be kind enough to correctly file it.