There are lots of questions related to this error but I think mine is a little different. I've got one non-consumable product and four consumable products in my game. Non-consumable product is used to unlock game levels and consumable products are used for in-game currency. A typical scenario.
Non-consumable product purchases work without problems but a majority of the users get "Cannot connect to iTunes Store" when they try to buy one of my consumable products.
EDIT: This is turning into a serious problem. Users are getting Cannot connect to iTunes Store error but it seems the purchases are successful. They are charged by iTunes Store. Any help is greatly appreciated.