CPW ports

Hi, in EMX I'm trying to define the ports of a CPW line as suggested in one document of the support area (i.e. P1:Gright,Gleft). The EMX simulation works fine. When I generate the schematic, I get this:

Basically, the two ground ports of each end of the CPW are properly defined as a unique node (e.g. G2_1, G2_2). 

However, when I try a simulation I get this error: 

I hope you can help me. Thanks.