On power up the sensor reads all the dip switch settings.  You must have at least one of the Magnet or Motion settings in the ON position for a sensor.  If none are ON it flashes this error sequence to let you know it’s not properly configured.  If it looks like your dip switches are properly configured just reinforce the dip switch settings and cycle power once again.  Anytime you change the dip switch settings you should do a power cycle by using the on/off power switch located by the batteries.