The RPS or Rotor Positioning Sensor error may manifest if there is no or bad feedback from the internal optical sensors in the DVR headstock.
Run low RPM will continually show on the screen if the motor consistently fails to reach a working RPM.
Follow the guide attached below for a step-by-step troubleshooting guide for resolving your RPS and Run low RPM errors. Depending on your circumstance the solution can be as easy as removing and cleaning the sensor.