Adding an onclick event to a div element

I’m not sure what the problem is; running the below works as expected:

<div id="thumb0" class="thumbs" onclick="klikaj('rad1')">knock knock</div>
​<div id="rad1" style="visibility: hidden">hello world</div>​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​
<script>
function klikaj(i) {
    document.getElementById(i).style.visibility='visible';
}
</script>

See also: http://jsfiddle.net/5tD4P/