I would say this is a mod_rewrite and permalink issue. If it was working before, then something changed with the host, maybe the .htaccess file in the forum directory, or the parent one. But, all you need to do to get around it, for now, is turn off the permalinks, to false.
This URL works fine for a second:
http://www.f1fanatic.co.uk/forum/forum.php?id=2
Then it redirects to a permalink URL:
http://www.f1fanatic.co.uk/forum/forum/motor-racing-discussion
Maybe you moved the forum recently and did not update the permalink structure?
No I haven’t moved the forum. The last thing I changed – which must have been a week ago or longer – was adding the following code into the .htaccess file for WordPress (not BBPress):
define('COOKIE_DOMAIN', '');
define('COOKIEPATH', '/');
Could that have had an effect? If so it seems odd that it took so long to manifest itself.
Thanks for the speedy response by the way 
OK I’ve tried changing the permalink settings and here’s what happens:
If I set them to ‘none’ – i.e. forums.php?id=1 the posts work
If I set them to ‘name based’ – i.e. /forums/first-forum/ the posts do not work
Obviously I would rather have name based if possible. Any thoughts?
I think you need to set up permalinks on your server if you want pretty or name based ones. False works fine, so it’s definitely a permalinks issue. Not sure why it was working before, but this is what needs to be done now:
https://bbpress.org/documentation/faq/#pretty-permalinks
Had the same bug, when I installed bbpress for the first time today. I noticed that it didnt even create the .htaccess file.
bbPress does not create the .htaccess file for you like WordPress does. I think in future releases they are considering creating it for you.
https://trac.bbpress.org/ticket/838
I have both WP and bbP using the same .htaccess file, in root. So, is this OK:
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress
Options +MultiViews
That won’t do anything at all for your bbPress installation I don’t think.
I am experiencing the same issues with my bbPress install. It was working fine before and I have not changed anything either. I figure the host (Dreamhost) has changed some configuration or other. I have contacted them and am waiting to hear back.
No word back from Dreamhost support, but it appears as if many DH customers are experiencing similar issues with other applications. I managed to fix my issue by logging into my DH account and changing the PHP version from 5.2.x -> 4.4.x and then back to 5.2.x.
Hope this helps someone
i have the same problem. if i change the permalink settings to name-based, some of the links (like editing profiles), return a 404 error).
matchfox: did you already try this?
https://bbpress.org/documentation/faq/#pretty-permalinks
If your site works without permalinks, it’s most definitely an issue with the rewrite rules.
https://bbpress.org/documentation/faq/#pretty-permalinks
This works for me!!
It’s a great script forum!
I’ve made some cusmotization, i can give you the url to see!
