Errors: not whitelisted and two metatags missing



I am experiencing some troubles with my twitter card. This is is the message that shows the card validator tool:

INFO: Page fetched successfully
INFO: 27 metatags were found
INFO: twitter:card = summary tag found
WARN: Not whitelisted
ERROR: Required meta tag missing (twitter:description)
ERROR: Required meta tag missing (twitter:title)

And this is the code I have posted in my header.php:

<!-- Twitter Card -->
<?php if(is_single() ) {?> <meta name="twitter:card" value="summary">
<meta name="twitter:creator" value="@NubITConsulting">
<meta name="twitter:url" value="<?php echo get_permalink(''); ?>">
<meta name="twitter:title" value="<?php echo get_the_title('Beneficios de la integracion de Dynamics NAV en Azure y en Office 365'); ?>">
<meta name="twitter:description" value="<?php echo get_post_meta($post->ID, '_aioseop_description', $single = true); ?>">
<?php if(get_post_meta($post->ID, 'og_img')){ ?>
<meta name="twitter:image" value="<?php echo get_post_meta($post->ID, 'og_img', $single = true); ?>" />
<?php } else { ?>
<meta name="twitter:image" value="" />
<?php } ?> <?php }?>

Please, could you help me out here?. I have no clue.

Many thanks in advanced.


What exactly does get_post_meta and get_the_title do? Seems like there is a problem with those.