Here is an example of how I used it and it works fine. in my case I am using a custom post type. Make sure you have the correct name for the custom field.
[display-posts include_excerpt=”true” tag=”tatag” image_size=”tour-guide” post_type=”profile” order=”ASC” meta_key=”wpcf-last_name” orderby=”meta_value” posts_per_page=”-1″]