ads momentum thick conductor up

I am designing a mixer and implementation is in microstrip. the substrate parameters are: εr=2.2, H=10 mil and T(cond. thickness) = 18 μm.
I've drawn the layout for co-simulation in momentum and am setting up thick conductor port definitions. after drawing on cond layer, set port definitions to single and internal as req.. then copied to cond 2 layer and am trying to put ports there s.t. the ports placed right above the ones on cond layer are defined as common mode associated with the port number beneath them. but when I do tht, an error message shows up: "Port P12 cannot cannot be associated with port number 1.
If they are in the same reference plane, and you want to associate them:
Please set both ports to the correct Port Type before
setting ^Associate with port number^". what am I doing wrong? any help would be appreciated.

P.S. for thick conductor, substrate has been defined as:
free space
strip cond 2----(cond thicknes T/2 = 9μm)
Air_metal Via Diel (perfect conductor)
Strip cond ----(cond thicknes T/2 = 9μm)
Given Substrate
GND

you should chose differential or gnd ref.
Share the design if possible.