Big black vertical bar on external screen
My monitor shows exactly the same black sidebar on the left. Tried many tips and tricks. And finally unplug the miniDP to VGA connecter on both side and reconnect again solve the problem. 

I tried to change the VGA side here and there for hours. :( so stupid me. So I guess some other also had the same experiences but I don't know why the answer is marked down to negative scores...

I didn't mean to solve all the problem for all. But just a mark for myself that shows it solved my problem and hopefully will help some of the others.