We have upgrade the magento 1.7 to 184.108.40.206 through magento connect from admin. After upgrading the version everything is working fine except the configurable product when I click add to cart button it will show "504 Gateway Timeout - The gateway did not receive a timely response from the upstream server or application." for existing configurable products. But when we add new configurable product it will working fine. Please help us to resolve the issue.