If I add a NetworkProximityChecker component to any gameobject (which does have a NetworkIdentity or a NI and a NetworkTransform) then I get an error with the client being unable to connect.
Everything works fine for the Host.
Unity 5.1.1f1
ArgumentOutOfRangeException: Argument is out of range.
Parameter name: index
System.Collections.Generic.List`1[UnityEngine.Networking.PlayerController].get_Item (Int32 index) (at /Users/builduser/buildslave/mono-runtime-and-classlibs/build/mcs/class/corlib/System.Collections.Generic/List.cs:633)
UnityEngine.Networking.NetworkProximityChecker.OnCheckObserver (UnityEngine.Networking.NetworkConnection newObserver) (at C:/buildslave/unity/build/Extensions/Networking/Runtime/NetworkProximityChecker.cs:44)
UnityEngine.Networking.NetworkIdentity.OnCheckObserver (UnityEngine.Networking.NetworkConnection conn) (at C:/buildslave/unity/build/Extensions/Networking/Runtime/NetworkIdentity.cs:328)
UnityEngine.Networking.NetworkServer.SetClientReadyInternal (UnityEngine.Networking.NetworkConnection conn) (at C:/buildslave/unity/build/Extensions/Networking/Runtime/NetworkServer.cs:1119)
UnityEngine.Networking.NetworkServer.SetClientReady (UnityEngine.Networking.NetworkConnection conn) (at C:/buildslave/unity/build/Extensions/Networking/Runtime/NetworkServer.cs:1064)
UnityEngine.Networking.NetworkManager.OnServerReady (UnityEngine.Networking.NetworkConnection conn) (at C:/buildslave/unity/build/Extensions/Networking/Runtime/NetworkManager.cs:697)
UnityEngine.Networking.NetworkManager.OnServerReadyMessageInternal (UnityEngine.Networking.NetworkMessage netMsg) (at C:/buildslave/unity/build/Extensions/Networking/Runtime/NetworkManager.cs:588)
UnityEngine.Networking.NetworkConnection.HandleMessage (System.Collections.Generic.Dictionary`2 handler, UnityEngine.Networking.NetworkReader reader, Int32 receivedSize, Int32 channelId) (at C:/buildslave/unity/build/Extensions/Networking/Runtime/NetworkConnection.cs:301)
UnityEngine.Networking.NetworkServer.InternalUpdate () (at C:/buildslave/unity/build/Extensions/Networking/Runtime/NetworkServer.cs:652)
UnityEngine.Networking.NetworkServer.Update () (at C:/buildslave/unity/build/Extensions/Networking/Runtime/NetworkServer.cs:514)
UnityEngine.Networking.NetworkIdentity.UNetStaticUpdate () (at C:/buildslave/unity/build/Extensions/Networking/Runtime/NetworkIdentity.cs:706)