I think you can put theses instructions in the SelectionChanged Event of the Calendar Control to prevent the selection of a second event:

 

 Private Sub Calendar_SelectionChanged(ByVal SelType As XtremeCalendarControl.CalendarSelectionChanged)
    If SelType <> xtpCalendarSelectionEvents Then Exit Sub
Dim TotSelect As CalendarViewEvents
Dim ViewEvt As CalendarViewEvent

dim i as long
    Set TotSelect = Calendar.ActiveView.GetSelectedEvents
    If TotSelect.Count > 1 Then

        For i=0 to TotSelect.Count - 2
             TotSelect.ViewEvent(i).Selected = False
        Next

    End If
End Sub

 

I would like to know how to let users select one sngle event only in the DayView.

 

Thanks!