It means that the PLC's current configuration has passwords disabled and you are trying to write a new configuration that has passwords enabled. Having passwords enabled is the default condition when you start a new project. It doesn't mean that you are using a password, only that you could if you wanted to. Disabling passwords is a safety mechanism that can prevent some unscrupulous person from applying a password to lock out legitimate users.
You have two options. You can disable passwords in your new configuration or you can clear the PLC memory. Clearing PLC memory will restore it to factory default settings which has passwords enabled. Once you've done that you will be able to download your new configuration.
