It's even more serious than...
Microsoft office access doesn't support this Activex control.
Actually it's :
Microsoft doesn't support this Activex control any more.
It was disabled because of security issues.
You can get round it if you are prepared to risk it..
see the last few posts here...
http://p2p.wrox.com/access/10416-rich-text-box-controls-access-2003-a.html