WordPress and phpBB3

I have a WordPress site, and I also have a phpBB3 forum on the same server. I’d like the two to share the same userbase. (e.g., you login in WordPress, it logs you in in phpBB3, or vice versa). I’ve tried to find a suitable plugin, but I can’t find one (I can’t seem to set up phpBB3 Single Sign On properly, and I’ve tried WP-phpBB Bridge, but that gave me an error when I try to go on the forum (I can’t access the site right now to give you the exact error code, but it says something about recreating a class on Line 24 of acm_file.php I believe)).

I’d really appreciate it if someone could help. Thanks