Is the .dll file still on your system ? (Search Windows Explorer). It may be corrupt, since I can't imagine it 'disappearing' altogether from one run to the next (but then this is Microsoff after all
).
Looks like you'll have to reload it either way. Probably easier to Remove OE and reinstall.
Seems you're not alone BRL, see:
http://www.generation.net/~hleboeuf/msoe.htm
(Edited to add link)