document.getElementbyId() returning null

You are executing your javascript code BEFORE the <div id="connectedUnregistered" /> was actually created.

Also note that you did not close your <div> with a corresponding </div>.

So move your javascript code to a part below your HTML. Or execute it after the page finished loading. If you are using JQuery you can do:

<script>

    $(document).ready(function() {

        ... your code ...

    });
</script>