I would like to create a set of web services that share a common set of types
(classes, structures, enums). I know I can create a VS 2005 web service based
on the Interface statement to contain these common types. The problem is that
I cannot determine how to create the implementation web services in a way
that I can cast the common types between proxy object parameters in a client
app. Please check the snippets of my code:

'Interface web service:
Namespace MyServices

   Public Class CallContext
       Public Environment As String
       Public Version As String
   End Class

   Public Enum Environments
       Dev
       UAT
       Prod
   End Enum

   <WebServiceBinding(ConformsTo:=WsiProfiles.BasicProfile1_1,
Name:="IWsDocuments", Namespace:="http://interfaces.MyCorp.com/")> _
   Public Interface IWsDocuments
       <WebMethod(), _
       SoapDocumentMethod(Binding:="IWsDocuments")> _
       Function ValidateConext(ByVal ThisCall As CallContext) As String
   End Interface

   <WebService(Namespace:="http://interfaces.MyCorp.com/")> _
   Public MustInherit Class WsDocumentsShim
       Inherits System.Web.Services.WebService
       Implements IWsDocuments

       <WebMethod()> _
       Public MustOverride Function ValidateConext(ByVal ThisCall As
CallContext) As String Implements IWsDocuments.ValidateConext
   End Class
End Namespace

'Sample implementation web service:
<WebService(Namespace:="http://interfaces.MyCorp.com/")> _
<WebServiceBinding(ConformsTo:=WsiProfiles.BasicProfile1_1)> _
<Global.Microsoft.VisualBasic.CompilerServices.DesignerGenerated()> _
Public Class Service1 '(other services: Service2, Service3, etc.)
   Inherits IWsDocuments.WsDocumentsShim

   ''' I use Shadows because compiler won't allow Overrides of web ref
object??
   <WebMethod()> _
   Public Shadows Function ValidateConext(ByVal ThisCall As
IWsDocuments.CallContext) As String
       If ThisCall.Version = "1.0" Then
           Return "OK"
       Else
           Return "This version not supported"
       End If
   End Function

   'Add implementation specific methods here:
End Class

'Client app:
       Dim cnc As New Service1Proxy.Service1
       Dim context As New Service1Proxy.CallContext
       With context
           .Environment = Service1Proxy.Environments.Dev
           .Version = "1.0"
       End With
       txtResults.Text = cnc.ValidateConext(context)

       Dim cnc2 As New Service2Proxy.Service2
       '''' Invalid Cast Exception occurs below:
       txtResults.Text &= vbCrLf & vbCrLf &
cnc2.ValidateConext(DirectCast(context, CncService2Proxy.CallContext))