How to setup Windows Server 2012 Remote Desktop Services to allow multiple users to connect to multiple servers

1. Start → Run → secpol.msc

   Security Settings\Local Policies\User Rights Assignment

   Right pane → double-click on Allow log on through Remote Desktop Services → Add Users or Group → enter Remote Desktop Users

2. Start → Run → services.msc

   Look for Remote Desktop Services and make sure the Log on account is Network Service, not Local System.

3. Check your event logs.

I believe what you are trying to do is install VDI. VDI required an AD domain with the Server 2008 schema extensions and in Server 2008 functional level even back at the time of its introduction in Server 2008. The requirement to have an Active Directory still stands with Server 2012.

You can install the Remote Desktop Session Host role without having an AD domain, though - simply use the "Role-based or feature-based installation" and tick the required roles instead.

Also, since you presumably have a Windows Server 2012 Standard license, you are entitled to running two virtualized instances of Windows Server without purchasing a further license. So you might choose to set up an additional VM running your AD DC, effectively enabling you to use VDI at the cost of 2 GB of RAM and 50 GB of storage (even less with de-duplication enabled) on your system.