What *do* you get instead of a 404? Something is probably overriding the 404 and displaying a page (WordPress does that sometimes depending on the way the theme is configured.) Are you integrated with WordPress?
And, can you post a link to your forum so someone can check the server response and see if it’s sending a 404 header but still displaying content? I recall that being a problem in the past but I can’t recall the details right now (maybe it was an IIS thing?)
I get the main (front) page. The url is bb.indieinvasion.net (by the way the server in running linux) Also I’m using wordpress integration
My guess is that there is something in the WordPress .htaccess file that is causing it to mess with what should be a forum 404 error. I don’t know enough about subdomains and bbPress integrated with WordPress, but that’s my guess. Something in the WordPress .htaccess file is rewriting your bbPress 404. Possibly? Is there a .htaccess file for bbPress? I would guess not, since you’re not using permalinks for the forum.
I suspect it has something to do with the subdomain, but that’s just a SWAG.