It's your IE security settings. If they are set to high, then the edit box wont display. Try medium-high under "Tools" > "Internet Options" > "Security".

More specifically, active scripting must be enabled.

Edit:
OK, I did some checking. The security issue is to do with a third party editor named FCKeditor, which looks like a great product btw. RCU added some really nice features with the new editor, but it requires a little adjustment to your security settings.