I suggest your portal is causing the issue as your cookie settings seem correct.
You really should update to the latest version, since you have no MOD's installed I suggest the following method:
*NOTE: Before proceeding backup all files and the database.*
- Upload all new files from a download of the full version, EXCEPT for config.php, the /images and /files folders.
- Go to yoursite.com/forumfolder/install/database_update.php
- Let that run and then delete the install folder.
- You now have a new up to date board containing all your users and posts but without any MODs that you might have had installed.
Please note: Any 3rd party styles will also require updating, style and board versions must match.