Symfony is not a valid entity or mapped super class.

Define the real entity:

 * @ORM\Entity

For example

Before :

<?php

namespace BookingBundle\Entity;

use Doctrine\ORM\Mapping as ORM;

/**
 * @ORM\Table(name="booking")
 */
class Booking
{

After :

<?php

namespace BookingBundle\Entity;

use Doctrine\ORM\Mapping as ORM;

/**
 * @ORM\Entity
 * @ORM\Table(name="booking")
 */
class Booking
{