I have several Magento stores hosted on bluehost. They had been running well for a couple of months and then suddenly one day the customers just could not add products to the shopping cart any more. The store just shows
Shopping Cart is Empty.
After days digging into the code, finally I found out the problem caused by
form_key that server side fetches stays the same for one session, but the
form_key on front side changes every time I refresh the page. So the
form_key passed from front end form is different from the one server uses to validate.
addAction() function always returns false and the items cannot be added to shopping cart.
I tried to block caching by adding the following meta tags to each page, but it did not solve the problem.
meta http-equiv="Cache-Control" content="no-cache, no-store, must-revalidate"
meta http-equiv="Pragma" content="no-cache"
meta http-equiv="Expires" content="0"