This function is a temporary fix for this wp-core bug: http://core.trac.wordpress.org/ticket/18614

Wordpress-Bug-Fix.php

function wordpress_fix_bug( $wp_query ) {
    // The function below is a temporary fix for this bug: http://core.trac.wordpress.org/ticket/18614
    if ( $wp_query->is_post_type_archive && $wp_query->is_tax ) {
        global $post_type_obj;
        $wp_query->is_tax = false;
        $post_type_obj = get_queried_object();
        if (empty($post_type_obj->labels)) {
            $post_type_obj->labels = new stdClass();
            $post_type_obj->labels->name = 'dev/hack to fix WordPress Bug';
        }
    }
}add_action( 'parse_query', 'wordpress_fix_bug' );