Trying to join two different IDs with AR

[eluser]spmckee[/eluser]
Here's what I'm using right now for the join part and keep getting: "Not unique table/alias: 'thug_client_groups'"

Code:

$this->db->join('thug_client_groups', 'thug_client_projects.group_id = thug_client_groups.group_id', 'left');
$this->db->join('thug_client_groups', 'thug_client_groups.company_id = thug_client_companies.company_id', 'left');