Balance 210 Active Directory Remote User Authentication

Has anyone managed to get this working? There does not yet seem to be any meaningful documentation on using Active Directory to authenticate Remote User VPN and no matter what settings I’ve used in testing and regardless of LT2P, PPTP, or OpenVPN, I’ve been unsuccessful in connecting. The event log of the Balance is showing this event constantly: L2TP/IPsec: Active Directory pre-authentication failed (K1:N255)

I had actually never done this before so just had a go. Did a clean install of Server 2012 r2 which is all I had to hand.

I followed this Radius setup guide which then authenticates against Active Directory: Configure a Radius server on Windows Server to authenticate Cisco VPN users | The Solving

Everything worked as expected. Let me know if I can help.