Jesse Friedman on "WP_Query in plugin throwing error"

I have a plugin that I'm writing. In the plugin I have the following class:

class aks_gf_augmentation {

	public function __construct() {

		$zip_code = '02653'; //this is temporary, eventually to be set by field filled out in gravity form

		$query = new WP_Query( array(
			'post_type' => 'aks_zip_code',
			'name' => $zip_code
		) );
		if( $query->have_posts() ) {
			while ( $query->have_posts() ) {
				$query->the_post();
				$rep_to_send = get_post_meta( $post->ID, 'aks_target', true );
			}
		}
		else {
			$rep_to_send = 'default@domain.com';
		}

		add_filter("gform_pre_send_email", "before_email");
		function before_email($email){

			global $rep_to_send;
			$email["to"] = $rep_to_send;
			return $email;
		}

	}

}

$aks_gf_augmentation = new aks_gf_augmentation;

The use of the 'post_type' argument in WP_Query throws this error:

Fatal error: Call to undefined function get_userdata() in /nas/wp/www/staging/agmoil/wp-includes/query.php on line 3911

If I remove the 'post_type' => 'amgo_zip_code' argument, the plugin doesn't return the correct post but it also doesn't thrown an error.

Am I missing something? I've never seen this error arise from using WP_Query in a plugin. Also I have double and triple checked that the name of the custom_post_type does = aks_zip_code

Any help would be greatly appreciated