sorry, i try your code , but it always return false........ eg(13/12/2011 or 12/13/2011)
how can i do to check date ?

Imports System.Threading
Imports System.Globalization

Public dateFormat As String = "dd/MM/yy"

    Function checkDate(ByVal c As String) As Boolean
        Dim d As Date
        Return Date.TryParseExact(c, dateFormat, CultureInfo.CurrentCulture, DateTimeStyles.AssumeLocal, d)
    End Function