Symfony Formular

I made my first steps in Symfony 3.x. I tried to make a simple small form, but I am getting an error message which I don't understand.

Variable "read_only" does not exist in form_div_layout.html.twig at line 323

My PHP:

use Symfony\Bundle\FrameworkBundle\Controller\Controller;
use Symfony\Component\Form\Form;
use Symfony\Component\Form\Extension\Core\Type\TextType;
use Symfony\Component\Form\Extension\Core\Type\SubmitType;

class StartController extends Controller            
{  
    public function testMeAction(){
        $form = $this->createFormBuilder()
            ->add('task',TextType::class)
                        ->getForm();

        return $this->render('psychoform.html.twig',array(
             'form'=>$form->createView()
        ));
    }
}

My Template:

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>  
 <body>                        
{{ form_start(form) }}     
{{ form_end(form) }}
</body>
</html>

What am I doing wrong? Thank you for your help. -Micha

"read_only" has been deprecated in Symfony 2.8, and instead should use read only as an attribute.

Symfony Github Issue Link

The issue must have occurred because of old symfony or twig version. Try updating both.