fix shipping method in eshop developed by zen cart

Hello The project is about locating and fixing a shipping feature in an eshop.. The website is [login to view URL] and is implemented with zen cart. The problem is that when you log in your account, and add a product in your cart, you should be able to choose the shipping method, either store pick up or shipping to your address. For some reason, suddenly, the second choice is not available. Note that this shipping method was working fine till recently. Sometimes it still works. We have not located the reason of the non stable behavior. The project is to locate and fix the shipping methods, so as the "shipping to your address" to be always available.