Garage door openers have required the addition of photoeye safety sensors since the early 90's.  These little items are by far the number one reason for service calls in the garage door industry.  Although they are a great system and do save injury or worst, that they are rather sensitive.  Most brand openers have sensors with a small LED light that indicates weather or not the cells are aligned and working properly.  If the beam is interrupted or if the cells are not facing each other and aligned properly, the door will not be allowed to go to the floor.  Most manufacturers will allow a bypass that will allow you to close the door with depressing and holding down the wall button.  This can be down from the inside and with the door in sight.  The remotes will not close the door at all, but will open the door.  Check for obstacles in the path of the door for proper alignment to possibly save yourself a service call.