Lotus Notes dictionary error

We have a user who gets the following error when trying to send an email, "cannot add word to dictionary." The error goes away if spell check is turned off but he wants to be able to use the spell check feature. This happens even if no words are misspelled. I've replaced his user.dic file, cleared out his cache and checked to make sure he can manually add words to his dictionary. He has full permissions to the data directory where the dictionary files reside. I found one article that said to move his temp and tmp directory locations which I tried but that didn't make a difference. Lotus Notes was removed and reinstalled on his system and nothing changed. Everything was working fine on his old computer and spell check has caused problems the entire time it has been on his new system.