Sears Craftsman / Door sensor issues

I just installed a Craftsman 1/2 HP garage door opener and everything works fine except the light / door sensors. After the door has opened and the light remains on for about 4 1/2 minutes, it goes out as expected. But....with the door open, if something breaks the sensor's beam, the light comes back on ( kinda of like a motion detector) and remains on for another 4 1/2 minutes and this activity repeatsd itself over and over again.