I suspect the cam on the euro lock is misaligned. Some cams are adjustable and some can slip. If you've ever had both keys in the door simultaneously and found the barrel just spins, feels tight and doesn't activate the lock this may be your cam slipping.
There is a certain rotational position of the barrel which will allow the key to be inserted and removed. There is also a certain position of the cam which rotates with the barrel (when working correctly) which activates the handle lock. If these 2 positions are "out of sync" you could end up with a situation where the door locks but the key wont turn far enough round to allow it to be removed. Ie the cam again strikes the locked locking mechanism which (because it's already locked) wont allow any further turning. The barrel has to be able to turn a full 360 degrees to be able to remove the key. I suspect that your lock engages almost straight away when you begin to turn and when it reaches 355 deg or so it is blocked by the locking mechanism.
Try putting a key in each side and fiddling to get the cam to slip. You'll feel it. Then try the lock to see if it now works. Alternatively, remove the lock by removing the retaining screw on the edge of the door and see if you can reposition the cam. It makes a bit more sense when you can see the cam on the barrel.
Chris, September 2009
