Sensor Error: Entry Sensor not responding

It means that the base sent a ping to that sensor, and did not get a response.  You could put the system in test mode.  The "ultimate" debugging scenario is to swap the failing sensor with another which is not failing.  If the problem follows the sensor, then the sensor may be bad.  if the problem stays with the location, than the location has a problem (too far away, too much walls and especially metal between the base and the location, or interference causing stuff near the sensor or between the sensor and base.