Modeling a WR-90 waveguide with one end embedded in a infinite PEC ground

Hello everyone,

I am a new comer of Altair community.

Recently I am trying to learn FEKO of Altair.

I started with a very simple example, modelling a commonly used antenna radiator, which is a WR-90 waveguide (22.86mm*10.16mm) with one end embedded in a infinite PEC ground to radiate energy into half free space.  When I complete the model and try to find its far field 3D pattern with the fundamental TE10 mode as excitation, a error box appears, which says

"The following message from the master process (MYID= 0):

ERROR 270: A triangle may not be located in the ground"

I have attached with this question the .cfs file of the model, could anyone help me to to find out the mistakes?

Thank you very much!