When the forum changed software a few years ago it caused a glitch with the insert part of the spell check that the administrators decided was more trouble than it was worth to fix. At the time RCadmin recommended IE Spell Checking, which is a free download.
http://www.iespell.com/download.php I have been using it for over two years with no problem and it is much better than the spell checker included in the forum. It allows the individual user to add words.
The Google tool bar also has a spell check.