From your description it sounds like the slide got off the track. Had a track problem from parking on a driveway. Slope was just enough to cause the tracks to separate. Went to a flat spot and kept moving the slide in and out in small increments while push the slide toward the track. Eventual got it back on track problem solved. Used a piece of 2x4 for a little gentle leverage. Didn't know what caused the problem until a year later parked on the same drive and put the slide out. 2nd time it took about 5 minutes.
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