Hi again Carlene
Further to my answer yesterday - I've spent a few hours on ours this morning and have identified the problem and have been able to repair it. Behind the release knob is a plastic block which operates the unlocking mechanism. This block is held in place by two small plastic buttons, one of which had broken off on mine. I was able to drill the plastic and replace the broken button with a small brass nut and bolt. Its now working fine - in fact better than original. I notice its a while since you placed your question so you may have already done something about it. If not - good luck.
Barry Kirkham., July 2009