What is not documented however is for single sign on to work by default, users must login with:
If a user logs in with just the user name such bugs.bunny as show in the screenshot below, when the user enters the RD Web Access and attempts to launch a remote application the user will receive the error below.
Your computer can't connect to the remote computer because an error occured on the remote computer that you want to connect to. Contact your network administrator for assistance.
Note: This error message is generic and is presented for a wide range of problems relating to RDS.
For my this Active Directory we want users to login by simply entering their username, we do not want users to have to specify their domain name. To do this perform the following procedure:
%windir%\Web\RDWeb\Pages\The Language of Your Location\