Dim enUS As New System.Globalization.CultureInfo("en-US")
If Date.TryParseExact(txt1.Text.Trim, "dd/MM/yyyy", enUS, System.Globalization.DateTimeStyles.AllowLeadingWhite, DateValue) Then
Dim dt As DateTime = DateTime.ParseExact(txt1.Text.Trim, "dd/MM/yyyy", System.Globalization.CultureInfo.InvariantCulture)
SqlDataSource1.SelectParameters.Item("date1").DefaultValue = dt
Else
MsgBox("Invalid Date")
End If