Quoting from the cited article:
In Word 2000 and above, you can sometimes fix this simply by clicking the
Start button in the bottom left of your screen, selecting Run, and typing:
winword.exe /a. (You may need to specify the full path although you probably
won't.) When using the /a switch in Word 2000 and higher, certain problems
with the Data key in the registry trigger a repair utility, and this utility
then automatically rebuilds the corrupt values. Such problems appear to be
strictly limited to bad settings in the Toolbars value, and the toolbar
settings have to be completely out of the range of "acceptable" values for
this self-repair procedure to be triggered; so mild corruption would not
usually be fixed by it.
If using /a doesn't fix the problem, or if you are using Word 97, you will
need to delete and recreate the corrupt registry value(s), as follows: