I think the engaging arm is getting over center and it gets screwed up. put a tarp strap on the upper end of the arm so it will not try to go over center the wrong way. Or maybe the idler pulley arm is getting hard to pivot and the spring that raises the pulley off the belt can't pull up the pulley to completly disengage the header. the grease zerk on the idler arm may need some extra grease. Make sure you can raise and lower the pulley easily. What about the belt guide that is fastened to the concave doorIJ If it gets tipped a little it will tear the heck out of the belt in a hurry. Also you must make sure the spring that keeps tension on the belt tight enough. There should be a flat piece of metal along side the spring to tell you if the spring is tight enough. With your cornhead you may need to tighen it a little more. Good luck.