Several things can be happening.
  1. Binding track isn't allowing free movement of the door. Could also be a lubrication issue. Lubricate the hinge points and rollers, then disconnect the opener and open/close the door a few times by hand to see that it's moving freely. Investigate any places that might seem stiff or binding.
  2. The opener is out of adjustment. There are two adjustment screws on the opener that control "UP" pressure and "DOWN" pressure. Turn the "down" adjustment screw slightly to increase the pressure the opener will exert before stopping.
  3. Electronic eye's protect the opening from kids, cars, and other things that may be across the doorway and prevents the opener from closing the door on these obstructions. Make sure the eye's are clean and pointing directly at each other. Make certain the wiring connections are tight at both the eyes and the opener, and check the wire along the way for any damage.
  4. The counter balance springs may need adjustment. I would recommend contacting a door repair company to make this particular adjustment because handling these springs is extremely dangerous if one does not know what they're doing.
Please report back your progress, we're always interested to know how things work out.