The (Insert New Time-Sheet) agent has a bug in the date format.

You can replace the existing code under the "Initialize" with the following, and it will work.

The only change is the addition of the "International" conditionals for the date format.

Sub Initialize
    
' =====================================================================
' Created By www.sbacode.com [Barbieri Fabio] - Groupware Team (c) 2006
' Project:
' Creato: 16 Ottobre 2006  by Barbieri Fabio
' Modificato : 16 Ottobre 2006  by Barbieri Fabio
' Note:
' =====================================================================
    
    On Error Goto Errore    
    
    Dim oWs As New NotesUiWorkspace
    Dim Mess$
    Dim oDocApp As NotesDocument
    Dim doc As NotesDocument
    Dim oSession As New NotesSession
    Dim oDb As NotesDatabase
    Dim view As NotesView
    Dim vDate As String
    
    Set oDb = oSession.CurrentDatabase
    Set oDocApp = oDb.CreateDocument    
    
    Do
        Call oWs.DialogBox ("DLG01", True, True, True, , , , "Insert NEW Time-Sheet" ,oDocApp,True,True)
        Select Case oDocApp.DLGUscita(0)
        Case "OK"
            Exit Do
        Case "ANNULLA"
            Print "Cancelled operation."
            Exit Sub
        Case Else
            Beep
        End Select
    Loop
    
    If Not setHolidaysDate( vDate , oDocApp.DLG_user(0) , oDocApp.DLG_monthYear(0)  ) Then
        Exit Sub
    End If
    
    Set doc = oDb.CreateDocument    
    doc.monthYear    = oDocApp.DLG_monthYear(0)
    doc.customer =    oDocApp.DLG_customer(0)
    doc.activity =    oDocApp.DLG_activity(0)
    doc.user = oDocApp.DLG_user(0)
    
    doc.month    = Month(oDocApp.DLG_monthYear(0))
    doc.year    = Year(oDocApp.DLG_monthYear(0))
    
    doc.form = "TimeSheet"
%REM
Set Authors Fields
%END REM
    
    Dim oName As New NotesName( oDocApp.DLG_user(0) )
    Dim vAuthors ( 1 ) As String
    
    vAuthors( 0 ) = "[Admin]"
    vAuthors( 1 ) = oName.Canonical
    Dim authorsItem As New NotesItem(doc, "docAuthors",  vAuthors, AUTHORS)
    
%REM
Set Readers Fields
%END REM
    
    Dim vReaders ( 0 ) As String
    vReaders( 0 ) = "[Supervisor]"
    Dim readersItem As New NotesItem(doc, "docReaders",  vReaders, READERS)
    
    Dim sData$
    For i = 1 To 31
        'sData  = Cstr(i) + "/" + Cstr(doc.month(0)) + "/" + Cstr(doc.year(0) )
        Dim international As NotesInternational
        Set international = oSession.International
        If international.IsDateDMY Then
            sData  = Cstr(i) + "/" + Cstr(doc.month(0)) + "/" + Cstr(doc.year(0) )
        Elseif international.IsDateMDY Then
            sData  = Cstr(doc.month(0)) + "/" + Cstr(i) + "/" + Cstr(doc.year(0) )
        Elseif international.IsDateYMD Then
            sData  = Cstr(doc.year(0) + "/" + Cstr(doc.month(0)) + "/" +  Cstr(i))
        End If            
        Dim dtGiorno As New NotesDateTime( sData )
        If Not Trim(dtGiorno.DateOnly) = ""  Then
            'Msgbox Weekday(sData)
            Call doc.ReplaceItemValue("Weekday_" + Cstr(i), Weekday(sData))            
        End If
    Next i
    
    doc.CF_Holiday = vDate
    Call doc.save(-1,-1)
    
    Print "Operation Finished With Happening."
    
    Exit Sub
Errore:
    Mess = "Errore   Agente: Insert  - Initialize  Riga errore : " + Str(Erl) + "  Definizione Errore : " + Error
    If Err Then
        Msgbox Mess        
        Err = 0    
    End If
    Exit Sub
End Sub