The error is a result of having Shadowbox open something when it wasn't ready.
For the head section, use this:
<script type="text/javascript">
    Shadowbox.init({
        skipSetup: true
    });
    window.onload = function() {
        Shadowbox.open({
            content: '#surveyDialog',
            player: 'inline',
            height: 450,
            width: 500
        });
    };
</script>
For the body section, use this:
<div id="surveyDialog" class="dialogWindowWrapper" style="display:none">
    <h2 style="color:#ffffff;">Hello!</h2>
</div>
For ready to use Shadowbox examples, visit the source page on github here.
EDIT: If you wanted to access the Shadowbox.open after the page has loaded, then check out the modified script shown here:
<script type="text/javascript">
    Shadowbox.init({
        skipSetup: true
    });
    function survery01(){
        Shadowbox.open({
            content: '#surveyDialog',
            player: 'inline',
            height: 450,
            width: 500
        });
    }
    window.onload = function() {
        survery01();
    };
</script>
Now that Shadowbox.open is in a named function, you can call it when required (e.g., use onclick attribute).