Clean it with detergent and water or even a little solvent on a rag.
Sliding screen door stuck at top.
Most sliding patio screen doors can be unstuck with a little maintenance.
The metal frame around the screen door is easy to bend and warp.
Almost all sliding patio doors are adjustable when it comes to height.
Again this is a fairly simple problem to fix.
If it fits too loosely in the tracks any vertical movement of the door will cause it to come unseated and it will fall.
First look at the lower track.
If the track is bent or squashed straighten it with smooth pliers and file.
Your door is old and worn out.
Remove the plug and use a screwdriver to tighten and loosen the roller height making very small adjustments and testing each time.
In some instances the sliding screen door will fall out repeatedly because it is too small.
If the edge of the door is hitting the frame try tightening the screws on the top middle or bottom hinge on both the door frame and the door being careful not to over tighten and strip the screws.
Most sliding patio doors have one or two small holes at the top and bottom of the door for adjusting the roller height.
Just opening or closing the door with too much force can warp the frame.
Determine exactly where the door is sticking before deciding on a remedy.
Locate the spring assembly which is often on the top.
To fix this you can adjust the height of the rollers by the screws on the rollers.