'GWM_FR_BCM_A_BUS' should be an immediate element of the input bus, not the input bus itself, right?
In any case, I would suggest you making the connection and selection manually first and then run get_param(CCF_Controller_base_path_2,'OutputSignals') to see what is the output.
Sometimes in a large model, the content of the bus is not immediately available after the BusSelector block is connected with the input bus. Maybe that is the cause in your case. You need to do a model update to make the content available. You can do this by
set_param(YourModelname,'SimulationCommand','update')