Following an upgrade to magento 1.8.1 on our development servers , we noticed that customers are unable to login to their account.
The issue is arising because the custom login form does not contain any form_key and there is a form key validation happening in loginPostAction of magento.
Here is the solution:
1 – Go to template/customer/form/login.phtml and template/persistent/customer/form/login.phtml and under
add the following code in the login form
<input type="hidden" name="form_key" value="<?php echo Mage::getSingleton('core/session')->getFormKey(); ?>" />
If you are using the login form in different templates then you use add the form_key to the other parts as well.
I hope this helps.
– We are aware that this issue also exists while updating the quantity of cart items, the same solution applies there.
– Previously there were two methods listed in this post to fix the problem but editing core files goes against Magento development standards so those instructions have now been removed.
If you need more help with Magento, see my extended post on how to configure a new Magento install for SEO.