couttsj:

In the Server project, in the ServerUI form, you have:

Code:
Private Function InitServer() As Boolean
    ReDim mServer(MaxClients)
    For lNum = 0 To MaxClients
        Set mServer(lNum).Callback(lNum) = Me
        mServer(lNum).IPvFlg = 4
    Next

End Function
Me in that case, invoked in a form, returns a reference to it, to that instance of ServerUI.

But in the SimpleServer Class, in the CallBack property Set, it expects a SimpleServer object reference, not a form:

Code:
Friend Property Set Callback(ByVal Index As Long, ByRef RHS As SimpleServer)
I found that when I just started to try to understand the issue discussed here.

PS: I would have expected the IDE to raise an error because of the type mismatch, but it doesn't.