Spell Checker Custom Dictionary

[tod]

How do you add a word to a custom dictionary. When I try I get the "Missing User Dictionary" dialog. It prompts me to configure one now and when I hit yes I just get the Spelling preferences pane which has a single checkbox for Enable spell checking that is checked and a line below that checkbox that reads "The selected spelling engine does not exist." Normal spell checking seems to work correctly, I just can't add any words.