oEditor is undefined... : Probleme in JS verification

Hi, im french so sory for my english

I have a big probleme in my back office.

I use PHP,JS and AJAX

I load a FCK editor texte area in basik mode with ajax in my page

the fck editor text area appear: i have 3 fck editor in this page they are loading correctly

whhit this code :

$oFCKeditor = new FCKeditor('evenement_description_courte');
               $oFCKeditor->BasePath = '/fckeditor/';              
               $oFCKeditor->Value = '';
               $oFCKeditor->Create();
$oFCKeditor1 = new FCKeditor('evenement_description');
               $oFCKeditor1->BasePath = '/fckeditor/';              
               $oFCKeditor1->Value = '';
               $oFCKeditor1->Create();
$oFCKeditor2 = new FCKeditor('evenement_lieu');
               $oFCKeditor2->BasePath = '/fckeditor/';              
               $oFCKeditor2->Value = '';
               $oFCKeditor2->Create();

And i use a verification for lenght in JS (if i can configure lenght of fck editor for each i would like know this )

function checkAddEvenement(id_form){

  oEditor = FCKeditorAPI.GetInstance("evenement_description_courte") ;
  oEditor2 = FCKeditorAPI.GetInstance("evenement_lieu") ;
  evenement_description_courte = oEditor.GetHTML(); 
  evenement_lieu = oEditor2.GetHTML();
  erreur = "";
  if (evenement_description_courte.length > 200){
    erreur = "Votre Description contient trop de caractere ("+evenement_description_courte.length+")";
    alert(erreur); 
  }else if(evenement_lieu.length > 128){
    erreur = "Le Lieu contient trop de caractere ("+evenement_lieu.length+")";
    alert(erreur);
  }else{
    submitForm(id_form);
  }
}

ADD Firefox tell to me :

oEditor2 is undefined
[Break on this error] evenement_lieu = oEditor2.GetHTML() ;

I tried a lot of thing but i dont find.....
I have some JS code with only 1 fkc editor + verification and i have no probleme... it's only if i have several verification in JS code

Please if u have an idea

Thx you for all reply and sorry for my english... i don't find the solution so