jquery validation not working after postback in asp.net

jquery validation not working after postback in asp.net

I am using jquery validation plugin in my asp.net page. In the codebehind if image size is big i am displaying an error in the aspx page. When I click "Register" button again the page is not getting validated again.
 
Can anybody help?

< script type ="text/javascript">

$(document).ready(

function (){

$(

"#<%=btnRegister.ClientID %>" ).click( function ()

{

$(

"#aspnetForm").validate(

{

rules:{
<%=txtName.UniqueID%>:{required:
true }
},

messages:

{}
 
});
});

});