Single Sign-on is not working with XenDesktop 7.x, and the Logon is unavailable.
This issue happens with both Windows Server and Windows Desktop OS type Virtual Delivery Agents. In the receiver options, the Logon Mode is unavailable as displayed in the following screen shot:
Install the latest Citrix Receiver 4.1 or higher available for download at http://www.citrix.com/downloads/citrix-receiver.html
The required process SSONSVR.exe is not running.