error msg of port is assigned to internal face for wave port in hfss

hi i am trying to simulate slotline to microstrip transition and for that i want to use waveport for microstrip line and for double slot line but i dont know why every time i got same error msg that port ids assigned to internal face.i am attaching my hfss model also paper from which i got idea of this balun plz if anyone can guide me about wave port?