Hello, i have the same problem : just after fresh install of stable 2.3.8 version, i can't login as admin, the page reloads to the login page.
I've tried to login many times, it worked one time only.
OJS is installed in a directory of the web root : /ojs/, i've an .htacces with the rewrite rules.
The Apache log shows many errors of the type : "client denied by server configuration: /home/htdocs/index" (/home/htdocs is the web root path).
Here is the Apache configuration for the /ojs/ directory :
<Directory "/home/htdocs/ojs">
AllowOverride All
Options Indexes FollowSymlinks
Order allow,deny
Allow from all
</Directory>
I've checked all ideas i've found in the FAQ and here, to no avail.
The browsers are accepting cookies (and they seems ok, with the real path). I've set the session_check_ip to Off
I've activated the MySQL debug option of the config.inc.php, it seems that the login is accepted then rejected ?
Thanks for your help

Edit : Same pb. with 2.4.1
Edit2 : More info. on the pb. With firebug i looked at the OJSSID cookie, and then at the sessions table. There i found that on the record corresponding to the sessions cookie value, the user_id field was 0, instead of 1 (admin user). When i change that value to 1, i'm recognized as the admin by the site. Not sure if it helps, perhaps the login process can't recognize my credentials ?