Problema con CLASES en ASP.NET

[Stream]

Código:

    Public Class Clsprueba
        Public Function sumar(ByVal x As Integer, ByVal y As Integer) As Integer
            Dim objMsgbox As New ClsMsgBox
            Dim suma As Integer = x + y
            If (suma > 10) Then
                objMsgbox.ShowMessage("La suma es: " & suma)
                sumar = suma
            Else
                objMsgbox.ShowMessage("Sobrepaso el limite")
            End If
            Return suma        End Function
    End Class