Mage::getModel('manufacturer/manufacturer')->xxx($_product->getManufacturer());

Call to a member function xxx() on boolean

$manufacturer = Mage::getModel('catalog/product')->getCollection()
            ->addFieldToFilter('manufacturer_name', array("eq"=>$manufacturerId))->getFirstItem();

Fatal error: Uncaught Error: Call to a member function getBackend() on boolean in /home/live/app/code/core/Mage/Eav/Model/Entity/Abstract.php:816