This read-only DisplayString holds the human-readable error text carried in the most recent Authorization Invalid message the Radio Slave received, returning an empty string if no such message has arrived since the last reboot. It gives an admin a plain-text explanation to pair with the numeric cwrBpiRsAuthInvalidErrorCode when diagnosing an authorization failure. For example, an admin investigating a repeated authorization rejection would read cwrBpiRsAuthInvalidErrorString for descriptive detail that the bare error code alone might not fully convey.