This error occurs when the TAP-Win32 network adapter has been disabled or is in use by another VPN application.
First, ensure you have uninstalled ALL other VPN applications and rebooted your machine after doing so.
1) Right click on the little computer screen next to your clock and click "Open Network and Sharing Center”
2) Go to >> Change Adapter Settings >> Right click on the TAP-Windows-Adapter-V9 and click Disable
3) Then enable it right away again and retry your VPN connection.
This should solve your problem.