Invalid argument when using embed code in single.php (but other embed codes OK)

Hi guys

Receiving this error after adding one of the Embed Codes to my single.php file for a field called Classification (it's a dropdown field in the back-end), the error is:

Warning: Invalid argument supplied for foreach() in /home/esanctuary/webapps/dubaimalls/wp-content/plugins/directory/themes/default/single.php on line 42

The URL is:
http://dubaimalls.esanctuary.webfactional.com/movie_listing/the-kings-speech

I have added other custom fields successfully using embed codes, eg the telephone number on this page:
http://dubaimalls.esanctuary.webfactional.com/listing/debenhams

Could it be anything to do with the fact that it's a dropdown field (which has been populated) and the telephone number is just a text field, this is the embed code that I'm using, copied directly from the Custom Fields page in the appropriate part of the Directory plugin:

<?php if ( get_post_meta( $post->ID, '_ct_radio_4db1e8d56211a', true ) ) { foreach ( get_post_meta( $post->ID, '_ct_radio_4db1e8d56211a', true ) as $value ) { echo $value . ', '; }} ?>

Would appreciate any help or advice you can give on why this might be happening

Thanks

Nick

(I'm using WordPress 3.1.1 and the latest version of the Directory plugin (downloaded today))