The TAP adapter is part of OpenVPN and important to establish a VPN connection. VPN connection is not possible without a TAP adapter.
The TAP adapter is installed together with OpenVPN during the installation of aLobby.
The following error message is usually displayed in the vpn.log:
There are no TAP-Windows adapters on this system. You should be able to create a TAP-Windows adapter by going to Start -> All Programs -> TAP-Windows -> Utilities -> Add a new TAP-Windows virtual ethernet adapter.
or:
All TAP-Windows adapters on this system are currently in use.
This solution is valid for Windows 7, Windows 8, Windows 8.1 as well as Windows 10:
After that you can establish a VPN connection to the siedler3.net server in the aLobby.
Reinstall the aLobby, making sure that OpenVPN is installed with the TAP adapter.