How to insert date value into a date type field using ajax calender extender

[Sandip Paul]

I want to insert the date into a date type field.My calnder extender format is "dd/mm/yyyy" and my system date format is "mm/dd/yyyy".
when date is less than 13th of any month then data inserted successfully but when date is greater than 12 the i got an error.
cs code

DateTime.Parse(txtvdate.Text).ToString("yyyy-MM-dd")

aspxcode

 <asp:TextBox ID="txtvdate" runat="server" CssClass="textb" MaxLength="15" Width="150px"></asp:TextBox>
                            <ajaxToolkit:CalendarExtender ID="vdate" runat="server" 
                                TargetControlID="txtvdate" Format="dd/MM/yyyy" Enabled="True">
                            </ajaxToolkit:CalendarExtender>