Magento 1.9 - Customers can't login to frontend [Page refreshes]

Question

Customers can't log into the frontend of the site after development.

The two test customers we used to test the site before the migration can login to the site perfectly but every other customer can't login. each time they try login the page refreshes. We know this is a cookies/sessions related issue but haven't found a solution to it yet. :(

We’ve tried multiple solutions recommended on the interntent, the most common of which is adding <input type="hidden" name="form_key" value="<?php echo Mage::getSingleton('core/session')->getFormKey(); ?>" /> to the login.phtml and flushing the cache.

Answer 1

check if browser has a second frontend cookie. If so setting a cookie domain in system config may help.

There are also more possible reasons. Is any FPC module in use?