F3 Cortex and Many to Many relation - orm

Question

I'm building a simple app using F3 and Cortex but I'm running in some problems trying to create a simple Many to Many relation. Its just two tables (and a third, from the relation), the tables already exist and have some data:
class User extends \DB\Cortex {
protected
$fieldConf = array(
'name' => array (
'type' => 'VARCHAR128',
'nullable' => false,
'required' => true,
),
'email' => array (
'type' => 'VARCHAR256',
'nullable' => false,
'required' => true,
),
'password' => array (
'type' => 'VARCHAR128',
'nullable' => false,
'required' => true,
),
// 'groups' => array(
// 'has-many' => array('Group', 'group_id', 'user_has_group')
// )
),
$db = 'db',
$table = 'user';
}
and
class Group extends \DB\Cortex {
protected
$fieldConf = array(
'name' => array(
'type' => 'VARCHAR128',
'nullable' => false,
'required' => true,
),
'description' => array(
'type' => 'VARCHAR128',
'nullable' => false,
'required' => true,
),
// 'users' => array(
// 'has-many' => array('User', 'user_id', 'user_has_group')
// )
),
$db = 'db',
$table = 'group';
}
accourind with this model of the database
But if I remove those comment marks, I get a strange error while acessing anything:
Internal Server Error
No valid DB Connection given.
And on refresh:
Internal Server Error
Fatal error: Leaked 1 hashtable iterators
It looks silly, but I searched all over and spent the better part of a whole day, and still can't seem to make it work.