calling javascript after databse validation??

[neomatrix2]

iam trying to call javascript on createuserwizard validation with following script

function ShowModalDialog()
{
 Page_ClientValidate();
 if(!Page_IsValid)
 $find('<%=AddUserValidationSummary_ModalPopupExtender.ClientID%>').show(); 
}

and my trying to call it for on pageload on create user button click event

btn.Attributes.Add("onclick", "ShowModalDialog();");

now it works but it fires blank for databse validation like duplicateusername

here is a screen shot when it fires for normal validators

[IMG]http://img32.imageshack.us/img32/3348/modalpopup1.png[/IMG] [IMG]http://img32.imageshack.us/img32/modalpopup1.png/1/w885.png[/IMG]

here is a screen shot when it fires for fraction of a second before database validation ..for which i hv couple of custom validators on my aspx page

[IMG]http://img17.imageshack.us/img17/9195/modalpopup2.png[/IMG] [IMG]http://img17.imageshack.us/img17/modalpopup2.png/1/w885.png[/IMG]

i want it to fire after after its over with databse validation like duplicate email..can anybody help me with that