If your greenhouse doors aren't running smoothly here are some of the things you can check:
When you close your doors, do they fully meet in the centre or are there any gaps
Are all the fixings tight and are all the parts fitted fully home & not loose
Is the ramp level, are there any high points under the ramp, the fin on the bottom of the door glides in the door guide and if you have a high point it will lift the ramp and cause the door to catch on the bottom
Check the wheels on the doors are running/turning freely in the top door track, clear any debris from the top door track
If the door is making a noise and not running smoothly, it could be due to a build up of dust/grit, if you run a screw driver up and down the black wool pile in the bottom door guide, this will remove any build up, if you then hose the wool pile this should clear remaining grit etc and the doors should run smoothly again for you.