No, my PHPBB and Zen cart are not in the same database. They never were. They still always worked.
I gave up on the integration because I couldn't get it to work... The sessions kept kicking each other out on the same page. I removed all of the code that was causing the problem. The logins still worked during that entire time, it just kept throwing "headers already sent" and a few other errors on the site home page, which has nothing to do with either the cart or the forum.
I tried switching back to the default template for the cart to see if my template edits were causing the problem. It still didn't work. My template shows the "forum nickname" box on the login page. Everything seems to work until you check the forum for the new user, which isn't there.
As I said earlier, I have the same cart with the same custom template on a backup server without the latest updates, but with the latest PHPBB and it still works perfectly. I've gone line-by-line looking for errors, but couldn't see anything.
I may try a fresh install of both the cart and the forum on the same site to see if it's in the database (I'll try switching between the old and new databases to see if there are any differences, I have an unlimited amopunt of databases on my server). This is the only site where it matters. The rest don't matter at all (in fact, more than one site only has the cart, no forum).
I'll update if and when I figure this out.
Ripper
Oz Website Services
https://www.oz-web.net