WPSC undefined JavaScript error.

While using Forms Authontication I met the following JS error "WPSC" object isnot defiend, and I added the following code then this error disappeared.

<script type="text/javascript">

if(typeof(WPSC) == "undefined"){

WPSC = new Object();

WPSC.Init = function(){

//do nothing
}

WPSC.WebPartPage = new Object();

WPSC.WebPartPage.Parts = new Object();

WPSC.WebPartPage.Parts.Register = function()

{
//do nothing
}

}

</script>