Unable To access Hidden variable from code behind

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C#

C#4.0

Hi,
when i access my hidden variable from my code behind iam getting the value as 0 instead of failed ,i checked by putting alert,its entering into the if loop.so no problem there.

function CheckDllsTxt() {
$('select').each(function () {
if (($(this).val()) == '-1') {
document.getElementById('<%=HdnValidation.ClientID%>').value = 'Failed';


}

});
<asp:HiddenField ID="HdnValidation" Value="0" runat="server"/>
i placed it both inside and outside of the update panel

C#:
ScriptManager.RegisterStartupScript(this, this.GetType(), "alertUser", "CheckDllsTxt();", true);
if (HdnValidation.Value == "Failed")
{
}
else
{
}
the Function CheckDllsTxt(); is also invoking,but iam getting HdnValidation.Value=0,pls help me out