2 x application server cannot install agent

Hi there,

I'm try to install terminal services following the guide but when I try to add new server (I'm using single mode TS under Windows 2012) I get the follow message:cannot install 2x terminal services on your local machine.
I have tried change credentials but even do it does'nt work. (I run the installation with administrator).
The machine is a Windows 2012 with Active directory.
I haven't found any reference that can help me so , I wrote this .

Regards
John