Normal.dot already in use

I am getting a dialog box stating that Normal.dot is already in use by
another user or application. I only get this message if I already have a
word document open and then launch Word from a third party application.
When I try to close the word document launched from the third party
application, I get the dialog box about Normal.dot. I've been running the
third party application for several months without any problems. So I'm
wondering whether there is some setting within Word that I modified that I
shouldn't have that has caused this problem.

Roger Marrs