This is a serious problem. Garage door rollers are supposed to sit well in the tracks in order to move up and down and carry the door to its full opening and closing position. By garage door roller off track, we actually mean that the roller(s) has found a way to exit the track. This usually happens when the garage door tracks are dented, bent or seriously damaged. It can also happen when the tracks are misaligned or tracks and rollers are not selected to match each other in terms of size.
When the rollers come off the tracks, the movement of the garage door will automatically stop and the door will jam. This happens because at least one of the rollers has escaped its normal route and it is stuck off the track. This problem requires immediate professional repair. When the rollers are off tracks so is the garage door! Consequently, the door will remain half open and be a safety hazard till it is fixed.