If you're using v1.5.x+ or have v1.3.9 and have an Admin Profiles addon installed, you'll need to create the user account and grant it some permissions.
Similarly, if you're using v1.5.0 you will need to create the user account, which involves assigning it a profile, then take the system-assigned user number and use that number when specifying the CRON_ADMIN_USER_ID definition.

Otherwise the script will be prompted to login.