Invalid Callback 'RWMB__Field'

Hi,

I am getting the following error:

( ! ) Warning: call_user_func() expects parameter 1 to be a valid callback, class 'RWMB__Field' not found in \wp-content\plugins\meta-box\inc\meta-box.php on line 63

As far as I can tell it only happens when i select “Option 2” in the code below. Any ideas?

array(
          'name'  => 'Options',
          'id'    => self::$prefix . 'Options',
          'type'  => 'select',
          'options' => array(
            'option-one' => 'Option 1',
            'option-two' => 'Option 2',
            'option-three' => 'Option 3',
          ),
        ),

*Please note values are for showing purposes only.

Thanks in advanced.

https://wordpress.org/plugins/meta-box/