rear brake install question

i am referring to this how to but have a problem. :http://www.mazdas247.com/forum/showthread.php?t=113741&highlight=rear+brake+pad+install

this is on a 2002 protege es with rear disk brakes. the allen key in the back of the caliper is turning but is not retracting. if we turn it clockwise the piston will come out further, but turning it counter clock wise it stops about a cm. shorter than it needs to be. the allen bolt still turns but the piston wont retract any more. any ideas?
 
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