Craftsman Pro toolchest gets stuck when locked???

I have had a real nice top of the line Craftsman tool chest for the past couple of years and EVERY time I lock the thing it gets stuck in the locked position so even when I switch to the unlocked position the doors will not open until I mess with it for about a half an hour until the doors finally open.
I have not needed to lock the chest until now so now it is areal issue. What the heck is going on and how do I fix it?
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