symfony2 Catchable Fatal Error: Object of class could not be converted to string
For Symfony 3.x
According with Symfony docs v3.x you should use choice_label property to specify the entity field name to be used here.
->add('categoryDescription', 'collection', array( 'type' => new CategoriesDescriptionType(), 'allow_add' => true, 'options' => array('data_class' => 'Apw\BlackbullBundle\Entity\CategoriesDescription'), 'choice_label' => 'name', 'by_reference' => false, ))