Require field validator disappear because of auto post of drop down?
<p>here is issue with my require filed validator , here i use one drop down box for select time with associated with require field validator in my drop down there are 1-24 hour time  and Select time with first index. in my page in drop down for time selection is necessary if user  select the time then again goes  the initial value of first index or select time option that time require field validator work and disappear immediately because of partial post back or auto post back of drop down.i have also use Update panel. i want that whenever user does not select time or choos select time option that time require field validator prompt user for select time. until user does not select time it cant process further.                      </p>

<pre><code>&lt;div class="loginBox"&gt;
                &lt;asp:Label ID="lblDateTime" Text="Date &amp; Time:" CssClass="jobTitle"   AssociatedControlID="txtDate"
                    runat="server"&gt;&lt;/asp:Label&gt;                    
                &lt;asp:DropDownList ID="ddlTime"  runat="server" AutoPostBack="true"   OnSelectedIndexChanged="ddlTime_SelectedIndexChanged"&gt;
                &lt;/asp:DropDownList&gt;
                &lt;asp:RequiredFieldValidator ID="rfvTime" runat="server" Display="Dynamic" ControlToValidate="ddlTime"
                    Text="Select Time" ErrorMessage="Select Time" InitialValue="-1" CssClass="ErrMsg"&gt;&lt;/asp:RequiredFieldValidator&gt;
            &lt;/div&gt;
</code></pre>
