for the error meassage:
Delete the Dreamweaver Cache file from the users configuration folder:
2 Authenticate User Behaviors:
If you set the Option to include the Remember Me checkboxes and to Auto Login, a second authenticate user behavior is created for the Auto Login.
No Captcha Image:
most likely the GD library is not enabled on your server.
if this is a local testing server, see the "Enable the GD Library setting on your testing server" tutorial on the learning resources page
if it;s a remote server, you will need to contact the host.