Patio Screen Door adjustment
It sounds like your door is coming off the track at the bottom.
First the few obvious things that you may or may not have already checked.
1. Make sure the track that the wheels roll on is clean and free of
dirt. If the track is dented or banged up your door won't roll as easy.
3.While it may look like your door is installed correctly on the track, visually inspect that both wheels actually are on the track. One wheel may be off track.
2. Make sure the wheels are adjusted up high enough to prevent the bottom of the door from dragging on the track. Use those adjustment screws to bring the door up as high as possible. This will load the spring brackets that hold the wheels and help keep your door on track.
You didn't say whether your door was old or new but if none of these
things help you, take the door off by lowering the wheels all the way, then lift the door up as high as possible and tilt it out at the bottom and remove.
Check to make sure that both wheels are in good shape and clean,
these wheels are plastic and can break. You can get replacements
at your local home center. They are ususally just held in with 1 or 2 screws.