This error refers to a problem with the sensor of the heated bed. It means that the sensor registers incorrect values and due to safety reasons it will prevent the heated bed from heating up. If you get a "MINTEMP error " it shows a too low temperature, while a "MAXTEMP error" suggests a too high temperature. The most likely reason for this is connection problem, which could happen due to a bad connection on the heated bed or main board, or damage of the sensor itself.

If you have access to a digital multimeter,please check the resistance settings on the head to see if the it's thermistor or resistor is blown. With the printer turned off and unplugged disconnect the hot end from the wiring harness and test hot end for the proper resistance.