How about  something like that:

DateTime dt = new DateTime();

DateTimeformatInfo dtfi = new DateTimeformatInfo();
            dtfi.ShortDatePattern = "dd/MM/yyyy";
            dtfi.DateSeparator = "/";

try

{

   this.SelectedDate = Convert.ToDateTime(value,dtfi).ToString("dd-MMM-yyyy");

}

catch

{

  //this would be default date if something was wrong

  this.SelectedDate =  DateTime.Now.ToString("dd-MMM-yyyy");

}

This should also work on all cultures.

Hope I understand your problem properly.