Security Assist will not create the database or the users table for you, you must create the database and users table before running the security assist wizard.
the undefined error can have many different causes.
How is the testing server tab of your site definition configured?
It can often be problematic to connect to a remote servers database within Dreamweaver, this is one reason we suggest using a local testing server for development.
See the Learning resources page for details on setting up a local testing server and setting up your Dreamweaver site for dynamic development:
the security assist wizard will be grayed out until you have configured a dynamic site in Dreamweaver, and created a dynamic page that is saved to the dynamic site. Have the new dynamic page open in Dreamweaver before running the wizard.