I ran openvpn client on my Ubuntu 14.04 successfully, but the sites with https (SSL protocol) cannot be opened while http sites seems working fine.
In case it will help someone, I got this error because I tried to connect to 2 VPNs at the same time. Usually I am using my own VPN that I have setup with OpenVPN on a Linux server to access Internet. For work, I had to use a VPN to access a few websites. However, I still want to keep my own VPN IP address to access most websites. So I tried to connect to the second VPN in an LXC container.
Only HTTP requests worked but HTTPS failed. The problem was fixed when I disconnected from my own VPN. In order to use 2 IP addresses at the same time, one for normal websites and the other for work websites, I used an SSH tunnel to my Linux server to browser normal websites through a proxy and used OpenVPN in an LXC container for work websites. It is also possible to use the OpenVPN connection as a proxy by creating an SSH tunnel to the LXC container.
At the moment I don't know if it is possible to use 2 VPNs at the same time without the HTTPS problem I had. I created a separate question for this issue: https://superuser.com/questions/1521812/use-a-proxy-or-another-vpn-before-connecting-to-a-vpn