OpenVPN Server error - Address not active
Cause
OpenVPN is running on this node, but it doesn't have the correct IP address.
Resolution
This is often because you've changed the VPN Address of the client.
OpenVPN doesn't re-load the client settings on the server until a timeout has expired (which is set to 60 seconds).  The easiest way to resolve this is to stop the openvpn service on the client, wait for more than 60 seconds, and then reconnect.  The following script can be run on the erroring node to resolve it:
/etc/init.d/openvpn stop
sleep 70
/etc/init.d/openvpn start |
While OpenVPN is down, you may get a different alert (saying OpenVPN is down), which can be safely ignored.