FortiGate Web SSL VPN gives "Connection Exception" error when trying to RDP to a Windows PC

I've finished configuring a Web SSLVPN on my FortiGate and created a few RDP bookmarks to my internal PCs. As per below, the bookmarks were nothing special and just using the Java based RDP (not native).

When it came time to test this out however, I keep getting the following error:

Connection Exception: Connection to remote desktop failed, please check network connection or remote computer configuration

Luckily the fix is simple.

By default Win8 and Server 2012 machines enable the 'Network Level Authentication' for remote desktop connections. Just goto the 'System Properties' of the machine and disable this tickbox (or push the change via group policy).

After this is saved I reconnect via the RDP bookmark and success!