Be sure that you are trying to access the intended area. By default, your PHP Live! system URL will display both the Operator and the Setup Admin login option on the same page. Be sure you are selecting the correct area you are trying to login at (Operator or Setup Admin).
The following documentation details the various URLs of the PHP Live! system:
Also, try the "forgot password" on the login screen if needing to reset the account password. If the "forgot password" is not working, contact the Setup Admin so they can reset the operator account password. If you are the Setup Admin and cannot login to the Setup Admin area, a reset of the password directly at the database is needed. The following Setup Admin password reset documentation details the procedures.