FCKeditorAPI.GetInstance fails in IE ?

I have a problem getting the Editor Instance via FCKeditorAPI.GetInstance in IE 6 and IE 7. The same script works fine in Firefox 1.5/2.0

I created the editor with this script:
...
<div id="editor-body" class="scrollbars">
<script>
<!--
var oFCKeditor = new FCKeditor('ed') ;
oFCKeditor.BasePath = '/FCKeditor_2_3_2/' ;
oFCKeditor.Height = "100%" ;
oFCKeditor.Value = 'This is some <strong>sample text<\/strong>. You are using <a href="http://www.fckeditor.net/">FCKeditor<\/a>.' ;
oFCKeditor.Create() ;
//-->
</script>
</div>
...

I see the editor working fine. Then I have a script which calls

editor = FCKeditorAPI.GetInstance('ed');

In Firefox I get the editor reference without a problem. IE throws the Exception 'Object doesn't support this property/method'

I debuged

alert(FCKeditorAPI.Version);
alert(FCKeditorAPI.GetInstance);

return proper values for Version and the function GetInstance. The inner array __Instances of FCKeditorAPI seems to be empty though.

Any idea how this is possible?

thanks alot.