So, I figured this out myself. It turned out to be a problem with pretty permalinks. The bbPress instructions for enabling pretty permalinks say, in part:
2. Create a file called .htaccess in bbPress’ root directory. Put only the following line in that new file.
Options +MultiViews
3. Try it out. If it doesn’t work, your web server does not support MultiViews.
I suppose I was thrown off because for the most part, it did work. When I tried the documentation’s alternative instructions — feeding the output of rewrite-rules.php into .htaccess instead of the MultiViews call — the broken links suddenly worked fine.
Hmm — forums/tags is being redirected to a page that exists, tags.php. But even navigating straight to tags.php causes the same error. I opened up tags.php in a text editor to see what was in there, and it referenced several files that don’t seem to be anywhere in my bbPress installation: bb_tag-single.php, tag-single.php and bb_tags.php. Could this be the problem? I downloaded a completely new copy of bbPress and couldn’t find them in there, either.
Here’s the tags.php code:
<?php
require_once('./bb-load.php');
bb_repermalink();
// Temporary, refactor this!
if ( !$tag && $tag_name )
bb_die(__('Tag not found'));
if ( $tag_name && $tag ) :
$topics = get_tagged_topics($tag->tag_id, $page);
do_action( 'bb_tag-single.php', $tag->tag_id );
bb_load_template( 'tag-single.php', array('tag', 'tag_name', 'topics') );
else :
do_action( 'bb_tags.php', '' );
bb_load_template( 'tags.php' );
endif;
?>
That was indeed the problem! Thanks a lot for the help.
