slt_cf_register_box( array(
    'type'  => 'post',
    'id'    => 'price',
    'title' => 'Price Option',
    'context' => 'normal',
    'priority' => 'high',
    'fields' => array(
        array(
            'name' => 'price-opt',
            'label' => 'Hide/Unhide price',
            'description' => 'Chose where hide or unhide price',
            'type' => 'select',
            'options_type' => 'static',
            'options' => array( 'Yes' => 1, 'No' => 0),
            'label_layout' => 'inline',
            'capabilities' => array( 'edit_posts' ),
            'scope' => array( 'post' )
        )
    )
));

//File: slt-custom-fields-display.php on line 271

//Substitute this
if ( $value == '[optgroup]' ) {
//with this
if ( !is_numeric($value) && $value == '[optgroup]' ) {