Asp – RaisePostBackEvent not firing

Use this:

<asp:CustomValidator runat="server" id="vld" ValidateEmptyText="true"/>

To validate an empty field.

You don't need to add 2 validators !

The thing is (if I understand your question correctly) that the control that calls the __doPostBack must implement IPostBackEventHandler interface. So, for example if I have this markup in a usercontrol (that implements the IPostBackEventHander):

<asp:Button runat="server"
     UseSubmitBehavior="false" ID="Button"
     Text="Update"
     OnClientClick="myfunction();"/>

The myfunction javascript must look like this:

<script type="text/javascript">
    function myfunction(param)   
    {
        __doPostBack("<%= this.UniqueID %>", "myargs");    
    }
</script>

Notice that I send this.UniqueID and not the Button.UniqueID because the button does not implement IPostBackEventHander but the usercontrol does.