Dale Arends says:

The first thing I would do is remove the track piece from the actuator and determine if the track parts themselves move freely and to the correct locations. If not, fix that. If they do, then look at the controller. When power is applied, does the gate move freely and to its correct limits? If yes, then check carefully for parts binding when the unit is reassembled. If not, try to determine if the problem is in the gate mechanism binding or if the problem is that the solenoid is no longer strong enough to throw the switch.

While you have it open, carefully clean any moving contact areas and re-lubricate it using as little lubricant as possible.