If the key enters the lock and turns a quarter turn anti clockwise but will not withdraw from the product, then this may be down to the ball bearings at the end of the lock bar not retracting when unlocked. This can be rectified by inserting the key and turning it into the unlocked position and then giving the cup a sharp tap with a hammer having first removed any plastic retaining caps (if applicable) this will cause the ball bearings to fall back into place. It should then be possible to remove the lock. Once this has been achieved, it is advisable to clean the ball bearings and the area around them with a wire brush and lubricate them with WD40.