I had the same problem as User login not work after SUPEE-8788 Patch
The suggested answers did not work for me, so I reversed the SUPEE-8788 Patch OK.
But still I cannot login to customer accounts. Why would that be?
I am using /template/persistent/customer/form/login.phtml as my login file.
I am also having an issue of not being able to login to admin after logging out. Again I have seen this linked to 8788 (php under 5.6 - I have 5.4). But still have issue after revert.
what is going on?
EDIT - this is not a duplicate of a question that I specifically referenced in my question that the result did not work. It is quite lazy to say this is a duplicate as if you read the quection you can see that answer has been considered and does not work. And I said I reverted the patch and still had a problem.