Cause
A USB-to-serial conversion cable must be used. The cable may be disconnected from the modem or GP. The modem may not be turned ON.
Solution
Check that the modem is properly connected. (GP → Serial conversion cable → Modem) Also check that the modem has been turned ON. Using the USB-Serial (RS-232C) Conversion Cable CA6-USB232-01 (optional accessory) for the connection between the display unit and modem is recommended. The following conversion cable can also be used.
Manufacturer: I-O DATA DEVICE, Inc. Model: USB-RSAQ3