Access denied for unpublished content in drupal 7
Few things to check for to figure out the problem based on your configuration:


Are you logged in or logged out while accessing the content?
Which user are you logged in with? Is this user the author of this content?
Check the permissions of this user (the ones related to unpublished content)...


Let us know if you need help or more details on any of the above.

Cheers.

UPDATE: if you want to customize the message that is displayed when access is denied, you can create a new page containing the custom message and then go to "Administration -> Configuration -> System -> Site information -> Default 403 (access denied) page" and set the path to your created page.