Opening the Session Setting dialog box, I cannot check the CSS checked -box. TS works without problem.
Using Window version 3.3.1016.772
On Window 7 64 bit machine
From your description, you have filled in the launch field. If so, is the launch process Java or a .NET application? Currently, the CSS feature doesn't work with Java or .NET applications. That enhancement is already planned, but currently is a lower priority than other features. Would it be important to you for us to move up the implementation?