Question about creating robotsystem from layout

Hi everyone,
    I am a beginner of RobotStudio. I am trying to create a robot system that contains a KUKA robot manipulator, a linear track and a positioner. I have imported the CAD model of each component and  created mechanism for each. But I am not able to create Robot System From Layout, it always said that 'The combination is not supported'. I have checked the manual about possible combination, but it doesn't mention the mechanisms that using external models. 
    Does anyone have encountered similar problem? Or does anyone could help me solve this problem? Many thanks from a struggling beginner.