$this->CI->load->plugin doesn't work

Hello,

I need to load an existing CodeIgniter plugin from my EE PlugIn.

This code doesn’t work:

$this->CI =& get_instance(); 
$this->CI->load->plugin('...the CI plugin');

Loading the CI Plugin via EE doesn’t work as well:

$this->EE->load->plugin('...the CI plugin');

Anyone any ideas?