Hide a bookmark with a ContentControlCheckBox

[Strange]

Hello,


I am new to MS VBA and i have a very special Question.
I am trying to hide a bookmarked text with a ContentControlCheckBox.

I tried this code:

Private Sub Document_ContentControlBeforeContentUpdate(ByVal ContentControl As ContentControl, Content As String)
      If ContentControl.Tag = "Checkbox1" Then
      If Content = "true" Then ActiveDocument.Bookmarks("Test1").Range.Font.Hidden = True
      If Content = "false" Then ActiveDocument.Bookmarks("Test1").Range.Font.Hidden = False
    End If
End Sub

But i just get an error message: Runtime error 6197: This object model error is not available in the current event.

What am i doing wrong? Can somebody help me with this?