product_info page not appearing

The site has been up and running for a couple of weeks now, but today we noticed that the product_info page is not appearing. Everything else seems to be OK, but when a user clicks on a product ID, nothing comes up. I know it was working this morning and I haven't made any changes for several days.

Any ideas?

http://shop.sacredmoondance.com
ver 1.3.8a

I restored my modules and template files from a backup and that fixed it for now.

Does anyone know of this happening before?