Error: Fehler beim Ausführen der Operation(VBA-OutlookKalender)

Set objApp = CreateObject("Outlook.Application")

' FTE_IsHoliday
' Fragt ab ob der Tag im Feiertagskalender steht
' @params [Date] datum [Datum des Termins
' @return [Boolean] Wenn ja true; wenn nein false
Public Function FTE_IsHoliday(ByVal datum As Date, ByRef returns As String) As Boolean
    Dim objApp As Application
    Dim objNS As NameSpace
    Dim objCalendar As MAPIFolder
    Dim objAppointment As Outlook.appointmentitem
    Dim sFilter As Variant
  
    Set objApp = CreateObject("Outlook.Application")
    Set objNS = objApp.GetNamespace("MAPI")
    Set objCalendar = objNS.GetDefaultFolder(olFolderCalendar)
    sFilter = "[Start] = '" & Format(FTE_TimeToZero(datum), "ddddd Hh:Nn") & "'"
    Set objAppointment = objCalendar.Items.Find(sFilter)
        If Not TypeName(objAppointment) = "Nothing" Then
            If InStr(objAppointment.Categories, "Feiertag") Then
                FTE_IsHoliday = True
                returns = objAppointment.Subject
            Else
             FTE_IsHoliday = False
            End If
        Else
            FTE_IsHoliday = False
        End If
End Function