If you can get over to the garage forum, DON 1 is a top notch expert on garage doors and openers and is very helpful.

Does the opener go into the obstruction mode where it stops and the lights blink? If so I suspect you need to adjust the sensitivity control. There is also an adjustment for the stop point when the door is closing.Your manual should have complete instructions for that and it is sometimes a seasonal adjustment. It's just a small knob or plastic screw on the opener, accessed without taking anything apart, where the home owner can make an adjustment as needed.

Another cause for the problem is a homeowner maintenance action item. The rollers bearings and any pivot points need oiling. I prefer to use WD40 a couple of times a year since in cold weather, the viscosity doesn't add to the resistance of opening and closing the door.

If the main light flashes 10 times when the door reverses it is a door sensor problem. Make sure they are pointed at one another and the small light on each one is lit and not flickering. Tweak them a bit. If you can't get both lights to come on you have bad wiring or one of the sensors has gone bad. One other thing you can check with the sensors is to make sure the sun isn't the culprit. When you are having this problem use something to shade the lens from the sun.

Now if the main light is not flashing 10 times you can try increasing the 'down force'. This is a control on the rear of the motor unit near where all those white wires go.