Because of the problem I  have, currently there is only code attached to a
"close button" on the form, so that nothing else can be the cause of this
problem.  The only item on the form for the moment is the close button.  With
another peace of code I am filling up the form with a tab-element with a few
pages (code attaced) It might thus be that the error I receive is due the
this bit of code?

The goal of this form is to create as much tabs as I have rec's in a
particular table.
Before adding pages, I first clear out all pages / tabelements.
The sub is thus used in a peace of code as following:

verwijdertabs "form1"
maakpaginas "form1", "subformame", 3

this is the sub:

Public Sub maakpaginas(formke As String, subformke As String, amount As Long)
   Dim i As Integer
   Dim frm As Form
   Dim aantal As Long
   Dim sjek As Boolean
   Dim ctltabset As Control, ctlpage As Control, ctlSub As Control,
ctlCheck As Control, ctlCheckLabel As Control, ctlCmd As Control
   DoCmd.OpenForm formke, acDesign
   Set frm = Forms(formke)
   

   Set ctltabset = CreateControl(frm.Name, acTabCtl, acDetail, , , 500,
500, 9100, 6100)
   ctltabset.Pages(0).Visible = False
   ctltabset.Pages(1).Visible = False
   For i = 0 To amount - 1
       Set ctlpage = CreateControl(frm.Name, acPage, , ctltabset.Name)
       ctlpage.Caption = "pagina" & i
       Set ctlSub = CreateControl(frm.Name, acSubform, , ctlpage.Name, ,
234, 1500, 9000, 4536)
       ctlSub.SourceObject = subformke
       Set ctlCheck = CreateControl(frm.Name, acCheckBox, , ctlpage.Name, ,
234, 1000)
       Set ctlCheckLabel = CreateControl(frm.Name, acLabel, , ctlpage.Name,
, 500, 970, 4500, 250)
       ctlCheckLabel.Caption = "Afgewerkt"
       Set ctlCmd = CreateControl(frm.Name, acCommandButton, ,
ctlpage.Name, , 2500, 800, 6770, 450)
       ctlCmd.Caption = "Maak registratie"
       ctltabset.Left = 200
       ctltabset.Top = 200
       ctltabset.Width = 9100
       Set ctlpage = Nothing
       Set ctlSub = Nothing
       Set ctlCheck = Nothing
       Set ctlCheckLabel = Nothing
       Set ctlCmd = Nothing
   Next i
   Set ctltabset = Nothing
   Set frm = Nothing
   
   DoCmd.Close acForm, formke, acSaveYes
end sub

thanks for helping out here!