The Authenticate User server behavior is set to use tyhe UserID column as the username column.
When running the security Assist wizard, you need to make sure the correct columns are chosen.
On the First Step of the wizard, make sure to select the UserID column as the Key Column.
On the third step, you will want to set the Username column as the unique column.
On the fifth step, make sure to select the Correct columns for the username and password column.
On the sixth step, you will need to select the correct columns for the email to address, the user name and the password as well.