Can't add words to the Dictionary when Spell checking

[Ian]

For some reason, the "Add" command is greyed out when I am spell checking the
document in Word 2000 such that I can't add a correctly spelled new word to
the dictionary to save repeated word error underlinings in red.

 

[Suzanne S. Barnhill]

The usual reason for this is that the language of the dictionary doesn't
match the language applied to the word. See the relevant portion of
http://sbarnhill.mvps.org/WordFAQs/MasterSpellCheck.htm