ReferenceError: Page_ClientValidate is not defined

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ASP.NET

jQuery

Hi,

I want to validate my page, if everything is filled.
However when do so I got this problem.

ReferenceError: Page_ClientValidate is not defined inside console panel of a firebug to identifier the problem,but I do not understand what is the problem:
this is my code :

<script type="text/javascript">
       $('#btnContinueChk').live("click", function (e) {
           e.preventDefault();
           if (Page_ClientValidate()) {
               $.checkSessionExists(function (event, data) {
                   if (data.sessionExists) {
                       PageMethods.ContinueChk($("#<%=rdoFreeStandard.ClientID%>").is(":checked"),
                       function(response){
                           var result = eval("(" + response + ")");
                           alert(result.Message);
                       });
                  }
                   else
                       window.location.href = urlpath + "Login.aspx?returnurl=" + encodeURI("MyProduct.aspx");

               });
           }
       });
   </script>

Please need some help...