getInstance method

hi guys!
I have a page where I create an instance of FckEditor.
Then I have a button (button1), when a click the button the div that includes the editor is hidden.
now, I have another button button2, and if I click on it I want to see again the fck editor.
the problem is that the first time my editor is correctly initialized, but the second time, the function getInstance return me the editor instance but I can't see anything.
This is my code:

HTML

  <div id="updF_noteOggettoDWH" name="updFieldOggettiDetail" style="display:block;">   
    <textarea id="fckNoteOggettoDWH" name="fckNoteOggettoDWH"><%=formatField(object.getNoteOggettoDWH(),"")%></textarea>   
    <input type="hidden" name="noteOggettoDWH" id="noteOggettoDWH" value="<%=formatField(object.getNoteOggettoDWH(),"")%>" />
 </div>

js to initialize the editor and on button2 click

   try {      
    noteEditor = FCKeditorAPI.GetInstance('fckNoteOggettoDWH');
   } catch (e) {
   }     
   if (noteEditor==null) {      
        noteEditor = new FCKeditor('fckNoteOggettoDWH') ;        
        noteEditor.BasePath = "../js/fckeditor/" ;
        noteEditor.ToolbarSet = 'MetadatiToolbar';
        noteEditor.ReplaceTextarea() ;   
   }  

js button1

document.getElementById('noteOggettoDWH').value = FCKeditorAPI.GetInstance('fckNoteOggettoDWH').GetHTML();

thanks!