Why did I open my mouth? Lol!

Problem here:

Images in my site have dissapeared! In my homepage, they are gone, they just appear if I enter a category and not all of them. In the products info pages, I have lost my images too.

In the admin, Im receiving this error when I enter to Catalog/ Categories / Products/ Product:


Code:
Fatal error: Call to undefined function: zen_calculate_image_size() in /admin/includes/modules/product/collect_info.php on line 474
Any ideas?

Thanks for your help!
Mike