are you talking your button is not working with the validation? try change your CausesValidation to true, cheer :)
<td align="center" bgcolor="#CCFFCC" class="style3">
<asp:Button ID="btnSubmitCheckup" runat="server"
onclick="btnSubmitCheckup_Click" PostBackUrl="~/NewCheckup.aspx"
Text="Submit Checkup" CausesValidation="true"
ValidationGroup="ValidationGroupDaw" />
</td>