A: 

Hi there,

This is how my setup looks like. It's for a Zend Framework app, but you should be able to translate it to CI with no problem.

try {
    Doctrine_Manager::getInstance()->setAttribute(Doctrine::ATTR_MODEL_LOADING, Doctrine::MODEL_LOADING_AGGRESSIVE);
    Doctrine_Manager::getInstance()->setAttribute(Doctrine::ATTR_VALIDATE, Doctrine::VALIDATE_ALL);
    $conn = Doctrine_Manager::connection($this->_db->getConnection());
    Doctrine::loadModels($this->_root . '/application/models');
} catch (Zend_Db_Adapter_Exception $e) {
    echo 'Incorrect database login: ' . $e->getMessage();
}

I would also check that all your references to where the models are loaded are correct. This kind of problem is usually caused by a bad reference to where your doctrine library is or where your models are.

Erik