Smart Problems

[kit2]

hi I have an old Smart42. I think its a central locking problem. I lock it and then when I unlock it again the car wont start. The engine turns over, and I have to get out, lock it, and wait for about 10 minutes then it starts normally. All day it starts normally then it will suddenly not start once or twice a day. The weird thing is, if I start the car with the door open it doesn't tend to happen as much. its really annoying having to wait 10 minutes. its defo not the engine, I thought it might be the battery but that seems ok, is it the central locking system, and is it possible to de-activate the locking system but obviously not de-activate the engine starting bit? sorry I don't know anything about cars but appreciate any advice. cheers.