This product is shipped with the password set as "Password: (None)".
In this case, click [OK] button without entering the password, the setup screen should then be displayed.

If you have set up a password in [Change in an administrator password] in the setup screen, you will need to enter that password in the password field.
Recheck your password and try again.
If you have forgotten your password, refer to [Setting Factory Default] to restore them to the factory default.