When trying to create a new box of my entity type from the blocks admin page, I am currently getting the following error message:

EntityMalformedException: Missing bundle property on entity of type entity_boxes. in entity_extract_ids() (line 7562 of /opt/local/apache2/htdocs/prototypes/boxes/includes/common.inc).

This error is being generated on a vanilla install of Drupal 7.15, with relevant supporting modules required for operation.