Recently I deployed Citrix XenApp 6.5 on virtual machines using a template I had previously created.  The machines provisioned without error, and appeared to be working properly.  Unfortunately, I was unable to open a remote desktop session onto the virtual server.  After researching the issue, I found a registry entry that corrected the problem.  I added a new DWORD called "IgnoreRegConfigErrors" with a value of "1" to the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server directory.

Other troubleshooting methods that may be useful are disabling any unused NICs on the server, and disabling IPv6 if using IPv4.