After checking for obstructions, if there is still a problem, check cable pulleys. I had to drive to Cape Coral, Fl. to help a Hi Lo with the same problem. The right rear cable had jumped one of the pulleys. We raised the top, braced it with a borrowed 2 X 4 (nice CG host) slowly lowered the top enough to take tension off the cable and put the cable back on the pulley. Raised the top and I held tension on the cable underneath with a rag as it was lowered, safe for travel. It was repaired at his home. New set of cables to replace stretched ones. New pulleys and bolts also. Good luck with your repairs!
Treeclimber