我从m_txtDateAdd获取值并发送xmlHttprequest

<asp:textBox id=m_txtDateAdd tabIndex=4 runat="server" Width="96px" Text="<%# Today %>">
</asp:textBox>

它有一个验证器

<asp:CustomValidator id="m_DateAddValidator" runat="server" ErrorMessage="Please Enter a Valid Date" ControlToValidate="m_txtDateAdd">&#x25CF;</asp:CustomValidator>

我的webmethod看起来像这样

[WebMethod]
public decimal GetTotalCost(DateTime transactionDate)
{
    String sqlDateString = transactionDate.Year+"/"+transactionDate.Month+"/"+transactionDate.Day;

我使用sqlDateString作为我发送到数据库的commandtext的一部分.它是一个遗留应用程序及其内联sql,所以我没有自由设置存储过程,并在我的代码后面创建和分配参数.这有效率的90％.在m_txtDateAdd的onchange事件上调用webservice.我一次又一次地从服务器得到的响应是

System.ArgumentException：无法将25/06/2009转换为System.DateTime.
System.ArgumentException：无法将25/06/2009转换为System.DateTime.

参数名称：type —> System.FormatException：String未被识别为有效的DateTime.

at System.DateTimeParse.Parse(String s,DateTimeFormatInfo dtfi,DateTimeStyles styles)
   at System.DateTime.Parse(String s,IFormatProvider provider)
   at System.Convert.ToDateTime(String value,IFormatProvider provider)
   at System.String.System.IConvertible.ToDateTime(IFormatProvider provider)
   at System.Convert.ChangeType(Object value,Type conversionType,IFormatProvider provider)
   at System.Web.Services.Protocols.ScalarFormatter.FromString(String value,Type type)
   --- End of inner exception stack trace ---
   at System.Web.Services.Protocols.ScalarFormatter.FromString(String value,Type type)
   at System.Web.Services.Protocols.ValueCollectionParameterReader.Read(NameValueCollection collection)
   at System.Web.Services.Protocols.HtmlFormParameterReader.Read(HttpRequest request)
   at System.Web.Services.Protocols.HttpServerProtocol.ReadParameters()
   at System.Web.Services.Protocols.WebServiceHandler.CoreProcessRequest()