Garage door comes up but not down using remote. Genie Blue Max?

It's probably a problem with the photocells/safety sensors. They are located near the floor on both sides of the garage door opening. There should be a sensor with a green light and a sensor with a red light. Both lights should be on steady at all times. If the red light is blinking, then check for an obstruction between the beams. If there is no obstruction check for misalignment of the sensors. If either red or green is out check for a short in the wiring. If there is no short then you may need to replace the sensors. Check www.geniecompany.com for troubleshooting and manuals.