Simulation of wilkinson power divider in CST

I tried to simulate the wilkinsson power divider at 5 GHz on 20 mil Ro4350b But my CST 2014 is giving following error:
The calculation domain is completely filled with metal (PEC). Please check background material settings and layer properties.
Adaptive port meshing failed.
please solve my problem and solve it if any suggestion. i am atttching CST project file also
My email:ldubey@gmail.comldubey@gmail.com

The error is what the message says.
You need to change the background material setting to air.