Silverlight not calling Javascript

Ive writting a simple Silverlight App which should call a Javascript function from the calling page:-
In Silverlight, Im using the code:-

                    HtmlPage.RegisterScriptableObject("Page", Me)
                    HtmlPage.Window.Invoke("slComplete")

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And then in my HTML page I have the following code:-

	<script type="text/javascript">
		function slComplete()
			{
			alert("Upload completed");
			}
	</script>	

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Yet, I cannot get the alert to appear :-(

Any ideas what Im doing wrong?