error converting datetime from character string

 Hi I am writing a sub on which I want to retrieve events from a database selected by a date. Using the calender for the selection date gives me an error 'converting date/time from character string' I have tried several thing but could not find a solution.
Can any one help! Thanks very much
Best regards,
Pieter Christiaan
Private Sub Calendar1_selectionchanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Calendar1.SelectionChanged
        Dim a As String
        Dim dd As Integer
        Dim yy As Integer
        Dim mm As Integer
        Dim cc As Date
        a = Calendar1.SelectedDate
        dd = Month(a)
&n ...