CiviCRM Message Templates link changed, cannot find
CiviCRM 4.6 has a new permission to edit templates separate from "Administer CiviCRM", and I'm almost certain the issue you're having is that you need to add permissions post-upgrade.

From your URL, I'm pretty sure you're running Drupal (and I think I knew that anyway!) so go to http://secularstudents.org/admin/people, select the "Permissions" tab, and locate the permission called "Edit CiviCRM message templates".  Check that off for the appropriate roles and press "Submit" at the bottom of the page, the problem should then be solved.