[TheLastSuperman]

Originally Posted by A84

Thank Rafa-el, my question was not if i had to change to something, but if i had to change just one, or both.

For those who might find this thread, the answer is:

- you must change them both. the /config.php file has "" assigned to cookie prefix, but apparently it is overridden as a default value somewhere. If you change it in /core/includes/config.php you have to change it in /config.php too (as stated in the config.php comment)

- in my case however, truncating the sessions table only did not work at all. In the end just to be sure, i truncated the table and changed both files. Hope this helps somebody in the future

Truncating the session table does work though, their session will end and they will need to login again before being able to post. What you should do in the future is close the site temporarily, truncate the session table then change cookie prefix and such, then truncate session table again and finally re-open the site which is the only way to ensure everyone is loading the new cookie per say.