Javascript can't change text in textarea once CKeditor instance as been called on it

Well i first wrote a Javascrip function that would change the text in a textarea according to the selection you made in a dropdown box, a really simple thing.

HTML

<form name="formconteudo">
<select name="selectpage" onChange="change();">
<option value="1">something</option>
<option value="2">another thing</option>
<option value="3">going crazy</option>
</select>
</form>

JS

var Code = new Array("", "Selected 1", "Selected 2", "Selected 3");
function change()
{
var ID =  formconteudo.selectpage.options[formconteudo.selectpage.selectedIndex].value;
document.formconteudo.ckeditor.value = Code[ID];
}

This worked pretty good and changed the text in the textarea. But then i called a CKeditor Instance on that textarea, so that i can use the CKEditor on that textarea. The Editor loads well and works great. But now the javascript isn't working.

Any hint on the problem?

Thanks