It sounds as if the template in which you are saving the toolbars is not being saved when you quit Word, and most likely this is the Normal template (both because that's the default save location for toolbars and because it's the one most likely to be not
being saved). The cause of this is usually a poorly written add-in, and ultimately it will be best for you to figure out which add-in is causing the problem and then, if you decide you can do with it, to remove it. As a temporary workaround, however, you can
open the Normal template itself, make the changes directly in it, and then manually save it.
If you know how to locate the Normal.dot template, then you can navigate to it and open it just as you would a document (you will see "Normal.dot - Microsoft Word" on the title bar, not "Document1 - Microsoft Word"). If you have difficulty finding the Normal
template, then here's another approach:
In Word, press Alt+F11; the Visual Basic Editor opens. Press Ctrl+G to activate the Immediate window. In that window, type
NormalTemplate.OpenAsDocument
and press Enter. Normal opens, but note that it may not be on top of all windows. You can close the Visual Basic Editor. Make the desired changes to the Normal file, and then save and close it. If the changes you have made have not been recognized as changes
(the Undo button is not activated), press Spacebar, then Backspace to "dirty" the file, thus ensuring that the template will actually be saved.