I disconnected the VPN and now I am unable to reconnect?
If you failed to disconnect correctly the system may still think you are still logged in, the system will see you are not connected after a few minutes and allow you to reconnect. If that fails to happen there is a fail safe system in place that clears inactive sessions every 15 minutes. If after that time you are still unable to connect try rebooting your computer.
If the problem persists it is always a good idea to try another connection type.