service openvpn start
Starting openvpn: [FAILED]

openvpn –config /etc/openvpn/server.conf –verb 6
Options error: Unrecognized option or missing parameter(s) in /etc/openvpn/server.conf:88: dh2048.pem (2.3.2)
Use –help for more information.

It means you forgot something.