Change date inside TextBox with TextBoxWatermarkExtender

Hi,

How can I change the date inside a TextBox with TextMode="Date" that uses a TextBoxWatermarkExtender?

I can't seem to do it from code behind:

<asp:TextBox ID="mailToDate" TextMode="Date" runat="server" Width="250px"></asp:TextBox>                                    <ajaxToolkit:TextBoxWatermarkExtender ID="mailToDate_WM" runat="server"                                        TargetControlID="mailToDate"                                        WatermarkText="Date"                                        WatermarkCssClass="watermarked" />

mailToDate.Enabled = true;                mailToDate_WM.Enabled = true;                mailToDate.Text = DateTime.Now.ToShortDateString();