Good Morning Simon,
Sorry for the trouble. The lightbox script that’s in the theme was a bit confused by the new version of jQuery that’s included with WordPress 3.6. The new jQuery is version 1.10.2, but the lightbox though that 1.10 was the same thing as 1.1 which caused it to break.
There are two ways to fix that. You can update the theme by going to the Updates section in your WordPress control panel and making the update there. Once you’ve completed the update, refresh your browser and that should fix it.
The other option is to look in the right hand column on this site and you’ll see a box called “WordPress 3.6 Upgrade.” In that box, there is a link to a quick plugin I made that will roll the version of jQuery included with WordPress back to the one found in WordPress 3.5. That should also fix the trouble.
If possible I would recommend going with the theme update.
Let me know if you have any questions or trouble.
Great looking site by the way.
Take care,
Bill