This error message means that no power has been detected on the reference voltage pin that can be found on

• Pin 1 (VTREF) for the ARM-20 connector:
• Pin 1 (VREF DEBUG) for the MIPI-10/20/34 connectors
• Pin 14 (JTAG-VTREF) for the Mictor-38 connector (if used for debugging)
• Pin 5 (VTREF) for the TI-14 and TI-20 Compact connectors

Please refer to ARM JTAG Interface Specifications for more information about the pin mappings of the different connector types.
Check list:

• Check if the target is powered
• Check if the debug cable is properly connected to the target, especially when an adapter is used (bad wiring)
• Check if the debug cable is connected in the correct way or is connected to the right debug connector if multiple connectors are available on the target board
• Measure the power on the reference voltage pin. Power must be greater than 0.9V.
• Check the target schematics:
  • Is the reference voltage pin properly connected to the JTAG header?
  • Is the GND pin correctly connected?
• Cross-check with another debug cable.