You are seeing this error because your parent/guardian account already exists and the system is trying to create a new one and detecting a duplicate.
Please try the following:
Please log in with your guardian account at go.njvs.org. If you don't remember your username and/or password, please click on the Forgot User Name / Password utility and enter your EMAIL address:
Please check your spam/junk folder if you do not receive the email.
Once you are logged in, please click CREATE APPLICATION on the left and enter the student's information.