I have some older sliding patio doors. Recently although when shut, pulling up the handle engages the mechanism, when I try to turn the key to lock the door, the key turns halfway then refuses to turn any further, no matter how hard I try. I removed the euro lock, and noticed that the tab that goes round was quite worn, so I replaced the lock. Unfortunately it still has the same issues. Anyone have any idea what it could be, or any troubleshooting tips.