Oscommerce error

I have an oscommerce site. It has been running for over a year. I recently had an issue come up. When you add an item X from the list of items it goes in fine. When you try to add another item Y into the cart it does not add it in but adds in another quantity for the X item. What is weird is if you add items from doing a search it works fine, but if you use the page links to get to a list of items it does this error of adding extra quanities to the 1st item entered and not adding in the other items to the cart.