Spell Check doesn’t work

Spell check doesn’t seem to be working since I upgraded to WordPress 2.7.

Here’s a preview of what it’s doing: https://william-hook.com/external/skitch/WordPress_2.7_Error-20081217-142300.png

The text it’s displaying is the HTML code of my 404 page (which is within the WordPress template itself), so the file it’s looking for is obviously missing. Or, as I presume, hasn’t got the correct permissions.

So, which file is it looking for and what permissions should I set?

Thanks.