Hi
The admins can't always tell a cover from an actual page without a clear statement, so if there's no "Cover" or "Page" in the title, it makes the job for the staff very hard while browsing through all the images. However your work meets with the standards in quality so please just send it again. We are happy to add it into our group. Just for the future remember to somehow point out that the cover really is a cover, not an actual page.
The staff apologizes for the possible inconvenience