I need to apply a custom validator to a text box to validate a date field, but when I run the code the event doesn't fire. 

Please Help!

Here is the code in the ASPX page for the txtDOB control

<tr>
                  <td class="SubHead" width="175">
                   <dnn:label id="plDOB" runat="server" controlname="cboYear" text="Date of Birth:"></dnn:label></td>
                  <td class="NormalBold" noWrap>
                   <asp:textbox id="txtDOB" tabIndex="13" runat="server" cssclass="NormalTextBox" size="25"
                    maxlength="50" Width="150px"></asp:textbox>
                           &nbsp;*&nbsp;
                            <asp:CustomValidator ID="valDateOfBirth" runat="server" ControlToValidate="txtDOB" OnServerValidate="valDateOfBirth_ServerValidate"
                                CssClass="NormalRed" Display="Dynamic" ErrorMessage="<br>Date of birth Is Required."
                                ValidateEmptyText="True"></asp:CustomValidator>
                            <asp:RequiredFieldValidator ID="valRequiredDateofBirth" runat="server" ControlToValidate="txtDOB"
                                CssClass="NormalRed" Display="Dynamic" ErrorMessage="<br>Date of birth Is Required."></asp:RequiredFieldValidator></td>
                
                 </tr>

Here is the code in the code behind

Protected Sub valDateOfBirth_ServerValidate(ByVal source As Object, ByVal args As System.Web.UI.WebControls.ServerValidateEventArgs)
            Dim valuePassed As String = ""
            Dim dt As Date

            If Not Null.IsNull(args.Value) Then
                valuePassed = args.Value
                dt = DateTime.MinValue
                args.IsValid = True

                Try
                    dt = Convert.ToDateTime(valuePassed)
                    args.IsValid = False
                Catch ex As Exception
                    args.IsValid = False

                End Try
            End If
        End Sub