login not working for customers and users after upgrade to 1.5.6.4

I'm trying to upgrade from OpenCart 1.5.1.3 to Opencart 1.5.6.4
but I cannot access anymore from admin or any user.
It happens with the default /install/ (upgrade) or any third party upgrade script.

I've not checked deeply the issue. Is there something changing in the login or hashes in those versions?
I didn't had such problems in other upgrades (I cannot remember the versions).

Thank you in advance.

why not installing the latest and best v.1.5.6.5, as virgin setup, and then make DB work ?
Would probably have been easier, especially, if you are still using old Extensions. Some of them
will no longer function anyway, since designed for v.1.5.1.x !?
Ernie
you could find it here:
http://www.evelo.li/shop/index.php?rout ... ation_id=4