I am having the same problem with my L7680. I have tried removing and reinstalling both the drivers and the Office suite to no avail.
I go into a chat session with HP tech support that redid everything that I had already tried and ultimately she said to disable all HP services in the MSCONFIG startup and reboot, if the problem still exists, contact MS. Well, it still exists.
Oddly, the error does not occur if I close the document before closing Word. It also does not occur if I create a new document and exit (whether I close it or not!