It might be that it is sensing too much resistance in trying to move the door. Possible causes might be a lack of grease in the tracks, or the springs counterbalancing the door may need adjustment. I usually disconnect the opener on mine and check freedom of movement by hand. It took a lot of tinkering to get my massive new door to work w/ an old, weak opener. If the door is open when you disconnect the opener, be very careful, as it may come crashing down hard if you have bad springs. Garage doors can be very heavy!

No its a new opener with a new house garage door. The garage door is very small basically meant only for one car park garage. the door moves well when it's released from the opener no problem there. Dont get me wrong the opener works but I hesitate and make sure it closes all the way. Out of 10 open closes sometimes it acts up.

I've tried many things, changing the force, amount of distance it should travel upwards - but nothing.

Oh also something else I should mention is that when it acts up I noticed the light bulbs on the motor blink really fast for about 10 seconds and then it stops. It's very wierd and it's only timetimes not all the time that this happen.

Anyhow if anyone has any ideas I would greatly appreciate it. Thanks

Sounds like the sensors in the doorway are not properly aligned. Tweak them a bit and try. Sometimes they are slightly misaligned and this will cause an intermittent situation.