Guessing there may possibly be restrictions to who your party can hold drop your party:
restrictions:
No duplicates
My PVP Party:
Mewtwo: cp 3871 psycho cut/focus blast 7x IV
Dragonite: 3581 steel wing/hyper beam 7x IV
Tyranitar:3578 bite/stone edge 7x IV
Salemence: 3269 fire fang/draco metero 90 IV
Metagross: 3131 zen headbutt /flash canon 91IV
Rhydon(rhypherior):3029 rock smash/stone edge 95iv (due to be higher cp and different moves once evolved)
My party is due to change depending how i feel. Possible Alakazam/Garchomp/(other)
Drop your party.
Also if Niantic decides to allow duplicates
my party:
mewtwo
mewtwo
mewtwo
mewtwo
dragonite
tyranitar