From looking at this, the line that is causing the problem (I think) is the following:

<div id="logo" class="back"><a href="http://www.thankyounature.co.uk/shop/"><img src="includes/templates/simply_kerrin/images/" alt="" /></a></div>

This would be in your includes/templates/simply_kerrin/common/html_header.php

It's telling IE that you have an image and a link here, but the line:

includes/templates/simply_kerrin/images is pointing to your images folder and an imagename would need to be added to the end of it.

If you have done no other modifications, just re-upload that particular (html_header.php) file from your simply_kerrin files..

On the demo there is a Zen Cart image there, perhaps you tried to change that?

Hope this helps :)