Visual Basic

'(VBA Code)
Public Sub Examine()
    Dim Item As MailItem
    
    For Each Item In Application.ActiveExplorer.Selection
        Dim Inq As MSInquiryNET.Inquiry
        Set Inq = New MSInquiryNET.Inquiry

           'Kontrolle ob Kunden-Daten in der Auswahl enthalten sind
            Set Inq.Item = Item
            Inq.CheckItem Item                 <--- WORKS (method of main class)
            MsgBox Inq.Medium                  <--- WORKS (property of main class)
            MsgBox Inq.Client.FirstName & " " & Inq.Client.FamilyName       <---- ERROR

        Set Inq = Nothing
    Next
    
End Sub

<Runtime.InteropServices.ComVisible(True)> _
<Microsoft.VisualBasic.ComClass()> _
Public Class Inquiry

    Public Function CheckItem(ByVal oMsg As Outlook.MailItem) As Boolean
        Me.Medium = GetMedia(oMsg)
        Me.Item = oMsg

        Try
            Select Case Me.Medium
                Case "PaperAds"
                    CollectScoutDataHTML()
                Case Else
                    MessageBox.Show(String.Format("Die Abfrage für '{0}' ist noch nicht automatisiert möglich.", Me.Medium), "Abbruch", MessageBoxButtons.OK)
                    Return False
            End Select
            Return True

        Catch ex As System.Exception
            MsgBox(String.Format("Fehler in der Routine '{0}'", "CheckItem"))
        End Try

    End Function

' main class' properties
    Private _Client As Client
    Public Property Client() As Client
        Get
            Return _Client
        End Get
        Set(ByVal value As Client)
            _Client = value
        End Set
    End Property

    Private _Item As MailItem
    Public Property Item() As MailItem
        Get
            Return _Item
        End Get
        Set(ByVal obj As MailItem)
            _Item = obj
        End Set
    End Property

End class

<Runtime.InteropServices.ComVisible(True)> _
<Microsoft.VisualBasic.ComClass()> _
Public Class Client

    Private _FirstName As String
    Public Property FirstName() As String
        Get
            Return _FirstName
        End Get
        Set(ByVal value As String)
            _FirstName = value
        End Set
    End Property

    Private _FamilyName As String
    Public Property FamilyName() As String
        Get
            Return _FamilyName
        End Get
        Set(ByVal value As String)
            _FamilyName = value
        End Set
    End Property

End class