Fail to import on existing project

Im using unity 5.5.1f1 and i have succesfully imported photon and photon voice chat into a new project. However I have an existing project that I will be adding photon functionality too. When importing the asset from the store, i get 2 specific errors everytime. This is happening on multiple computers, and different versions of unity.

the error reads...

Assets/Photon Unity Networking/Editor/PhotonNetwork/AccountService.cs(121,22): error CS0122: `AccountService.registrationCallback' is inaccessible due to its protection level

Assets/Photon Unity Networking/Editor/PhotonNetwork/AccountService.cs(121,22): error CS1955: The member `AccountService.registrationCallback' cannot be used as method or delegate

Any insight to why i might be getting this error??