Hi Mauricio!
Let me first of all thank you for being so quick to respond and all the work you've put into the integration!
To rule out any other problems, I have just performed a completely fresh install of DNN 4.8.4 running on IIS in WinXP with .NET 3.5, Database is SqlServer 2005 (not express). I only added your version 2.0.1 beta of the FCKEditorProvider as explained in the install notes, i.e. copy the dll to bin, remove the old FCK folder and copy in the new one.
The editor itself is the new version and functions perfectly. But I still cannot change from the basic text editor back to the richtext editor once I've switched. I get exactly the javascript error I explained in my previous posts.
The radio buttons actually do not even belong to the Text/HTML module, but to the basic DNN texteditor control, that is used throughout various modules that allow rich-text editing. I checked the problem using the Text/HTML module, but I can also reproduce it using the MLHTML module.
I believe, my offered solution would not interfere with any other components. But I'm astonished you could not reproduce the error. I used Firefox 3, but also checked in IE7, Opera 9 and Safari. All show the same behavior.
Regards
Christoph