Mark Days at Runtine

First you have to selekt the evebt, then you can do what you want with this event:

Private Sub calCont1_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single)

Dim TerNr As Long
Dim CaEvt As XtremeCalendarControl.CalendarEvent
Dim CaEvs As XtremeCalendarControl.CalendarEvents
Dim CaHit As XtremeCalendarControl.CalendarHitTestInfo
Dim ViEvt As XtremeCalendarControl.CalendarViewEvent
Dim ViEvs As XtremeCalendarControl.CalendarViewEvents

If Button = vbRightButton Then

Set ViEvs = CaCol.ActiveView.GetSelectedEvents
For Each ViEvt In ViEvs
    If ViEvt.Selected = True Then
        ViEvt.Selected = False
    End If
Next ViEvt

Set CaHit = CaCol.ActiveView.HitTest
If Not CaHit.HitCode = xtpCalendarHitTestDayViewTimeScale Then
    If Not CaHit.HitCode = xtpCalendarHitTestUnknown Then
        If Not CaHit.ViewEvent Is Nothing Then
            TerNr = CaHit.ViewEvent.Event.id
        Else
            TerNr = 0
        End If
    Else
        TerNr = 0
    End If
Else
    TerNr = 0
End If

If TerNr > 0 Then
    CaHit.ViewEvent.Selected = True
    CaCol.Populate
End If

End Sub