Same problem as Harbor Freight hitches. The hook doesn't stick out far enough. The pins holding the hook hit the implement frame before the hook engages.
See modifications here:
http://www.tractorbynet.com/forums/attachments/252974-quick-hitch-problems-post2944942.html#post2944942
Bruce
See modifications here:
http://www.tractorbynet.com/forums/attachments/252974-quick-hitch-problems-post2944942.html#post2944942
Bruce