I can't get getdata to work. It gives me the error "Variable 'Data' is passed by reference before it is assigned a value." What is wrong with it?

Code:
    Private Sub ServerSocket_DataArrival(ByVal sender As Object, ByVal e As AxMSWinsockLib.DMSWinsockControlEvents_DataArrivalEvent) Handles ServerSocket.DataArrival
        Dim Data As String
        ServerSocket.GetData(Data)
        serverlogtxt.Text = serverlogtxt.Text & "[" & Now.ToLongTimeString & "]" & Data
    End Sub