I've just encountered a problem with viewing additional pictures. Everything uploads fine and the product page looks exactly as it should but when I click on the additional image only the main image loads up.

I have other products that have additional images that I entered ages ago and they work as they should. It seems that it is only new products that are experiencing this problem. I've cleared out my cache and restarted my browser (I've even tried different browsers) but I can't get the additional images to load.

As this is a feature I only use occasionally I don't know when this problem started. I have upgraded from 1.3.8 to 1.5.0 to 1.5.1 so this could have happened at any point along the line.

Can someone advise me how to fix this or point me to the relevant code so I can check it?
Thanks