Most garage door openers have a feature that when they encounter too much resistance, they will reverse. This is to prevent the door from trapping/crushing something that didn't get out of the way (a car, person, or your dog). It sounds like the door isn't jamming completely, but it is just "rough" in one spot of the travel, which kicks the the opener into reverse.
Do you have the option of shutting the door manually? In my garage, there is a latch that lets me disconnect the door from the opener, which allows me to slide it up and down by hand. Try opening/shutting the door hand and see if it feels "tight" at the point where the opener would reverse.
If you can identify a spot where this happens, you have something off in your door/track.
If not, something is wrong with the garage door opener.
If it is the opener, some things to look at:
Some openers require periodic
lubrication of the screw drive
mechanism (not the door track). Find
the manual for it and see if there
are any reccomendations for greasing
it. There may also be crud in it,
preventing a smooth travel.
The electronics inside the opener
that detect a jam may be
malfunctioning. If so, good luck
finding replacement parts.
One other things to note: Did it suddenly get cold out? Thermal expansion properties of the door and track can trigger problems.
What is the condition of the batteries in the remotes? Make sure that you have good fresh batteries so that a strong signal gets to the garage door opener base unit.
Also evaluate if it is possible that something has changed in the area around the garage door main unit. Have you recently placed some large metal object nearby that may affect the RF signal path from the remote to the base unit. Maybe an alumimum extension ladder or a metal storage cabinet.
Lastly is it possible that a neighbor may have a similar model opener to yours and it uses a "rolling code" security feature. Your opener could be picking up some stray signals from their opener and making yours get out of sync with your transmitter dongles.
Best Answer
I had this issue with a house and the root cause for me was sunlight interfering with the sensors. It only happened in the summer for about 3 hours of the day when the sun was just right to overwhelm the light beam receiver. My fix was a cardboard tube mounted around the receiver to provide addition sun light blocking so it could see the light emitter. You can also try swapping the emitter and receiver.