onMouseMove Problem into Editor

Hi, I have a image that show some description when user move mouse over, using onMouseMove event.

The script for event is inside of Editor something like this:

<p><img height="216" src="/_userfiles/Image/01.jpg" width="289" alt="" onMouseMove="test();"/></p>
<script language="javascript">
function test(){
//window.parent.document.all("Explain").innerHTML = "Some description for image..."
alert("Some text for example...in forum")
}
</script>

In a previus version RC3, it´s not problem, but, with this new version FC2, fail.

it is a new restriction for that version? can everyone help me?
thanks.