VPN Server fails to start - could not not read Private Key password from stdin

Hi all,

I recently got a new image for my Raspberry-Pi. I got it flashed to the SD-Card and after the initial config task I installed the openvpn package.
I followed the instructions to setup the server and did: sudo service openvpn restart
To be save I issued a reboot afterwards and when the system was back 'systemctl -status openvpn' shows everything ok

Now I tried to connect with the Android OpenVPN Client (with the newly created mynetwork.ovpn file) but the connection fails with: Connection Timeout.
So I checked the openvpn server lock and saw:

Mon Apr 18 15:03:53 2016 us=304445 ERROR: could not not read Private Key password from stdin
Mon Apr 18 15:03:53 2016 us=304671 Exiting due to fatal error

So the VPN server tries to read the private key password from stdin ?
The previous Pi-Ubuntu didn't had that issue!

How to solve this probelm ?