fckEditorInst.CreateHtml() is not a function

<div id='pageHTMLfck'> <img src='nieuw.gif' onLoad='ShowEditor("<?= $row['comment']) ?>")';> </div>

function ShowEditor(HtmlSourceCode)
   {
   var fckEditorInst = new FCKeditor('pageHTMLEditor', '100%', 300, 'CustomAjax', HtmlSourceCode);
   fckEditorInst.BasePath = "properties/FCKeditor/";
   document.getElementById('pageHTMLfck').innerHTML = fckEditorInst.CreateHtml();
   }