The background worker crashed with an exception present on some devices. This crash cannot be fixed by the app itself.
Either try restarting the app and if that doesn't help try restarting your device.
If the problem persists and your device is rooted try downloading the app Tun.ko Installer as it might be able to fix it. The developer of this app is DroidVPN Inc.
Link: https://play.google.com/store/apps/details?id=com.aed.tun.installer