[leone184]

There is a set of photo-eyes that are mounted near the bottom of your door frame, one on either side. If one doesn't pick up the other's signal, it thinks there is something under the door and will refuse to close it. This would explain the sudden reversal, and the flashing light. I've never heard of sunlight causing a problem, but I suppose it's possible. Make sure the eyes are properly facing each other, they could be off a small amount, which might only make a difference when there is lots of sunlight shining on them.

Could there be some moisture inside one of the units? Perhaps the direct sunlight is heating the area up, making a small amout of water vapor condense on the lens, obscuring it.

Also check the staples that hold the wires up, it sounds unrelated, but sometimes the vibration will cause a staple to rub thru the insulation and cause a problem. (even after 4 years)

One more thing: after the problem is solved, turn down the "downward force" adjustment back down to the minimum needed to close the door properly. If its set too high, the unit will continue to push down even after the door contacts the ground. (or anything else, like someone's foot) This will put a lot of extra wear and tear on the opener and the door.

leone184