I'd start by releasing the door from the trolley and operating it manually to observe where it is snagging, loose or misaligned. Also make sure the springs on both sides are working properly and not significantly stronger on one side than the other, as well as that the track is secure at all attach points.

Thanks for the reply.
I notice that the cable has 1/2" more play on the left side (the side that snags one quarter of the way up) you have to hit the remote 2 /3 times to get it to go up - one side is 15" the other (snag) is 15 1/2" Maybe when I changed the rollers (especially the last one the holds the cable) I threw the cable out of wack? How do I make up the slack?
Also I changed the rollers because I found berrings on the floor. But did not see where the rollers had openings for the berrings to fall out - could it be the berrings were actually from the pullys - I could not see any openings in the pullys (but not really knowing where to look from up on the ladder).
Thanks again
Bill

OK - fixed the problem - it was one of the pullys - that's where the berrings came out of - new pully and all is well
Thanks Randy - its amazing when you know where to actually look for the problem.