Error 91: Object variable or With block variable not set

Dear friends,

I get a message from someone who performs a test for me that message above emerges when opening my vba project. Below is the code. I'm puzzling, but can't find the solution. In my excel 2007 and 2013, the error doesnt appear. Is there anyone who can help me?
Here's the ThisWorkbook code:

Private Sub Workbook_Activate()
    Application.DisplayFullScreen = True
With ActiveWindow
.DisplayGridlines = False
.DisplayHeadings = False
.DisplayWorkbookTabs = False
.DisplayHorizontalScrollBar = True
.DisplayVerticalScrollBar = True
End With
End Sub

Private Sub Workbook_Deactivate()
    Application.DisplayFullScreen = False

End Sub

Private Sub Workbook_BeforeSave(ByVal SaveAsUI As Boolean, Cancel As Boolean)
MsgBox "Opslaan is niet toegestaan" & vbNewLine & "Copyright", vbCritical + vbOKOnly, "KomKids"
Cancel = True
End Sub

Private Sub Workbook_BeforeClose(Cancel As Boolean)
          ThisWorkbook.Saved = True
MsgBox "Hartelijk dank voor het gebruik van de rekentool van KomKids!" & vbNewLine & vbNewLine & "Graag tot ziens!", vbOKOnly + vbInformation, "KomKids"
End Sub

Private Sub Workbook_Open()

Sheets("START").Visible = xlVeryHidden
    Application.DisplayFullScreen = True
With ActiveWindow
.DisplayGridlines = False
.DisplayHeadings = False
.DisplayWorkbookTabs = False
.DisplayHorizontalScrollBar = True
.DisplayVerticalScrollBar = True
End With

MsgBox "Welkom bij de Rekentool 2014 van KomKids!" & vbNewLine & vbNewLine & "Na het invullen van uw gegevens worden uw" & vbNewLine & "bruto en netto kosten per opvangsoort berekend." & vbNewLine & vbNewLine & "KomKids brengt geen feestdagen in rekening." & vbNewLine & "Uw netto eigen bijdrage kan daarom lager uitvallen dan deze berekening toont." & vbNewLine & vbNewLine & "Vul hierboven eerst uw basisgegevens in.", vbOKOnly + vbInformation, "KomKids"
End Sub

It appears after clicking "enable editing" in Excel 2010+. That is right after shutting down the protected view.