load balancing client error?

Im trying to just simply import photon voice from the asset store and this is happening. I can import it cleanly on a new project but on an existing project i get this error. any insight to why this might be happening? im using unity 5.5.1f1

Assets/PUNVoice/Scripts/PhotonVoiceNetwork.cs(370,51): error CS0070: The event `ExitGames.Client.Photon.LoadBalancing.LoadBalancingClient.OnOpResponseAction' can only appear on the left hand side of += or -= when used outside of the type `ExitGames.Client.Photon.LoadBalancing.LoadBalancingClient'