Had the exact same problem on my car with the door skin added. Turned out to be the Mini door handle plunger was pressing very slightly against the Z3 mechanism. You'll need to reach inside the door with a flat screw driver and push the plunger outwards to relieve the pressure. You should hear it click and the door will open. Once you've opened it you'll need to trim the plunger to give a couple mm clearance. It is something to do with the central locking and it thinking the car is being broken into !
A pain in the arse and took me ages to suss it out. Jaguartvr pointed me in the right direction , he had the same thing too !
Last edited by Lucky@LeMans; 31st May 2020 at 23:03..