How to use comparevalidator to compare date in ASP.NET 3.5?

In designer,

<asp:CompareValidator ID="cvReturnDate" runat="server"

                            ControlToValidate="txtReturnDate"

                            ErrorMessage="Return date must be valid date." Type="Date"

                            ValidationGroup="validateInquiry" >*</asp:CompareValidator>

In Code,

                    this.cvReturnDate.Operator = ValidationCompareOperator.GreaterThan;

                    this.cvReturnDate.ValueToCompare = DateTime.Now.ToShortDateString();