MessageBox and BubbleEvent

Hello,

I am trying to open a MessageBox for some particular Customers in the A/R Invoice form (139). When pressing the button Add, a message box should ask, if the freight is allready added, if not, the invoice should not be added, otherwise yes.

Surprisingly, my code works, if I use the MsgBox from VB.net, but not the MessageBox from SAP. What do I need to know about the SAP message box?

Does anybody have an idea?

Does not work:

If SAPbouiCOM.IApplication.MessageBox("All OK", 2, "Yes", "No") <> 1 Then
    BubbleEvent = False
End If

Works:

If MsgBox("All OK", MsgBoxStyle.ApplicationModal Or MsgBoxStyle.YesNo, 
          "SAP") <> MsgBoxResult.Yes Then
    BubbleEvent = False
End If