Object doesnt support this method using destroy()

Hi, my english is bad, but i'll try to explain you:

I have several elements with click event assigned. clicking on them, shows the ckeditor with information taken from a database. everything works fine until there.
but when I click 2 times on the same item I get an error despite destroy the instance if it already exists:

I got this error:
"Object doesnt support this method"

well, this is the code

onComplete:function(r){
$('blog_box').set('html',r);
var _target=$('blog_box').getElement('textarea').get('id');
var o=CKEDITOR.instances[_target];
if (o)
o.destroy();
editor=CKEDITOR.replace(_target);
}