if it is selected then ...

What is litCalendario01?  A Control, which type of control exactly (button, checkbox, ...)?  Please explain further.

it's a button

In that case what "is selected" represent for you?  You could use multiple button events:On Click, On Got Focus, ... it truly depends what you want to happen and when.  Please explain the user experience you are trying to achieve here.

I don't understand your code as you seem to be hiding the control if it is 'selected'?

there are a txtbox i called "txtDataProssimaUdienza" (its a date type, but i disabled the calendar because i needed to disable Saturday and Sunday)  and a button i called "litCalendario01" (the calendar connected to txtDataProssimaUdienza).
litCalendar01 isn't visible untill i get focus on txtDataProssima. When i lose focus on txtDataProssimaUdienza litCalendar01 isn't visible, but i can't click on it to open the calendar.
This is the code for txtDataProssimaUdienza

Private Sub txtDataProssimaUdienza_GotFocus()
    litCalendario01.Visible = True
End Sub

Private Sub txtDataProssimaUdienza_LostFocus()
    If litCalendario01 Then
        litCalendario01.Visible = True
    Else
        litCalendario01.Visible = False
    End If
End Sub

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and this is the code for litCalendar01

Private Sub litCalendario01_Click()
    Dim strFrmName As String
    strFrmName = "DatePickerCalendar"
        DoCmd.OpenForm strFrmName
            With Forms(strFrmName)
                Set .prpCtrlInitialDate = Me.txtDataProssimaUdienza
                .fSetUp
                .Caption = "Prossima Udienza"
            End With
End Sub

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