Many details lacking, such as OS, version of IE/OE (6 or 7) and if you happen to have installed Office 2007.
It seems that Office 2007 is incompatible with Outlook Express 6.0 as admitted by Microsoft in http://support.microsoft.com/kb/932974/en-us
It could be the problem is solved if you upgrade to IE7 (it isn't mentioned). And it could be that you need a third party spell check tool, as (remarkably!) advised in that Microsoft article.
Here's another link about it: http://ask-leo.com/outlook_express_spell_check_broke_when_i_upgraded_to_xp_how_do_i_fix_it.html
It shows a huge increase in this error message (including the french variety) after the release of Office 2007.
Hope this helps.
How do you change the language on Outlook Express? Only drop down I see in spell check is French and I want to change to English.