Controller.php

public function whateverAction()
{
    $form = $this->createForm(new ViewingReportType($viewings));
		
    $form->bindRequest($this->getRequest());

    if($form->isValid()) {
        die('valid');
    }

var_dump($this->getFormErrors($form));

    return $this->render('PhoenixCRMBundle:Something:index.html.twig', array( 
        'form' => $form->createView(),
    ));
}

MyFormType.php

class MyFormType extends AbstractType
{
    public function buildForm(FormBuilder $builder, array $options)
    {
	
        $builder
			->add('introduction', 'textarea', array(
				'required'      => true,
				'property_path' => false,
			))
		;
    }

	public function getDefaultOptions(array $options)
	{
// REMOVING THIS METHOD GETS RID OF THE ERROR
		$collectionConstraint = new Collection(array(
			'introduction' => new NotBlank()
		));

		return array('validation_constraint' => $collectionConstraint);
	}
}

Output

array (size=2)
  0 => string 'The fields "introduction" are missing' (length=43)

Template.html.twig

{{ form_row(form) }}