Error 645 - Internal Authentication Error
This problem tends to occur when using Windows 98 or Windows ME. This can be resolved by following these steps:
  • Recreate the Dial Up Connection as described here.
  • Windows 95/98 - This error can occur if the Require encrypted password option is enabled on the Server Types tab in the connection's properties, or an incorrect user name or password have been entered. See MS KB Article Q199780
  • All versions of Windows - This error can occur if you are attempting to connect to a Windows 2000 domain that has had a RRAS (Routing and Remote Access Services) server log on without administrative privileges. See MS KB Article 227747