DateTime に変換すると、次の例外が発生します。
String was not recognized as a valid DateTime.
lbl_RequestDate.Text = "13/2/2013";
CultureInfo provider = CultureInfo.CurrentCulture;
string[] format = provider.DateTimeFormat.GetAllDateTimePatterns();
Follow.RequestDate = DateTime.ParseExact(lbl_RequestDate.Text, format, provider, DateTimeStyles.None);