user/logout access denied v7.34
Try different way 


This works for me if I substitute the logged-in username for 'user', like this:


http://my_site/my_user/logout

ie:

http://example.com/jdoe/logout


this might be problem with not enabling clean url in your site go to 


http://example.com/admin/config/search/clean-urls 

enable clean url and check if its working 


as you mentioned use http://example.com/user/logout will logout the current user section


Further readings:
logout problem - https://www.drupal.org/node/1572984

enabling clean url - https://www.drupal.org/node/1572984

access denied + logout - https://www.drupal.org/node/2192401