Error 645 - Internal Authentication error
  1. Make sure customer has put in there username/password.
  2. If the customer is Ex-directory and CLI is not enabled use the CLI fix - Properties of connection - remove area code in dial properties - put 1470,,0845 in the telephone number box - before the dial up number.
  3. In properties of connection - server types - remove tick from encrypted password box.
  4. Remove dial up adapter from control panel > networks - reboot and re-install.