Automated login with LDAP always returns error
Perhaps not a direct answer to you question about the LDAP module but I managed to enable SSO in a Windows domain environment with the Webserver authentication (https://www.drupal.org/project/webserver_auth) module. 

You need to force Windows Authentication in your IIS site and disable Anonymous authentication. The Webserver authentication module is also capable of creating accounts when a Windows Domain user is visiting your site and is not registered in Drupal.