This has gotten so far,that I will sum up what we found out:
Inside the event handler the attribute src cannot be read in IE8 (FF works fine), neither with
the problem is not in the attr('src') but in something else. The following snippet works in IE8:
<img id="xxx" src="yrdd">
<script type="text/javascript">
alert($('#xxx').attr('src'));
</script>
But if you for example change the the text/javascript to application/javascript - this code will work in FF but will not work in IE8