Hi Bonnie,

thanks a lot für your advice. I changed my code to using an interface, but the problem still occurs.
This is what I do now:

The cmdexit-button-class changed to

        If TypeOf (Me.Parent) Is IDoExit Then
            CType(Me.Parent, IDoExit).DoExit()
            MsgBox("Interface Button")
        Else
            'MsgBox("Methode fehlt")
        End If
        MyBase.OnClick(e)

The Myform-Baseclass-Code is now

Implements IDoExit
...
   Public Overridable Sub DoExit() Implements IDoExit.DoExit
        If Not Me.lIsRunning Then
            MsgBox("Interface Base doexit")
            Me.Close()
        Else
            MsgBox("Interface Isrunning")
        End If
    End Sub

As you mentioned, I forgot to say that all forms are inherited from that myform-baseclass.

Form1 which is the startform, has two buttons, the inherited cmdexit-button which closes the form and another button which
start Form2 as a modal form.
When I click the cmdexit-button on Form1 everything works, i get the "Interface Base doexit"-msgbox and the form closes.

Form 2 has also a cmdexit-button and I expected it to close this form too. But what it does is, that it shows first
the "Interface Base doexit"-msgbox, then the "Interface Button"-msgbox (which does not happen on Form1) but does
not close the form.
So something must be wrong in my inheritance chain.

Best regards

Thomas