The main purpose of the sliding screen door is to slide on the track, if it falls off then the screen is not working properly and need to be fixed. You should not have to force the screen across the opening, if it is sticking or getting caught it probably needs to be adjusted. Sometimes the rollers are not metal and may be worn down.
If the screen door is fairly new and the wheels are not raised enough for the screen to glide right it will fall off track and stick. Try reaching over at the bottom raising slots which are next to the roller and with a fillips screw driver turn clock wise to lift the patio door, if this does not help then you may need to have a mobile service come to your home and give you a free estimate. I service: Thousand Oaks, Lynn Ranch, Westlake Village, Oak Park, Agoura Hills, Lake Shearwood, Newbury Park, Camarillo, Conejo Valley, Moorpark, Happy Camp, Santa Rosa, Pleasant Valley, Simi Valley, Woodranch.