I've been tracking an issue in one of our WP installations and keep coming up short of a solution.
One of our websites is installed in a sub-directory of our main website. Both are WP installations.
We noticed several weeks ago that in the child site, when a user (logged in or otherwise) posts a comment, he is returned a 404 for wp-comments-post.php. The file does indeed exist, and I've tried replacing it with a known working copy, chmod values, etc. The only thing that I can do to get comments working is to remove (entirely) the .htaccess file.
Assuming it was a permalink issue, I started playing with settings there. If I change the permalinks setting to default, I can indeed get comments working alongside the .htaccess file. Any other permalink format and I'm back to the issue (until I delete the .htaccess file of course). The default permalink setting isn't a viable solution as we have so many linked blog posts out in the wild. We don't want to risk breaking those.
I've played with various .htaccess rewrite rules to see if I can get around this, but keep coming up with nada. The vanilla .htaccess settings that get generated when I save permalinks doesn't help. I have a hunch that it's related to the nested directory structure - the child site living within another WP installation directory. All the literature I find says that shouldn't be a problem though.
The site in question is a Genesis theme put together by a designer who is stumped.
Another oddity, is that we randomly get 404 errors while navigating the admin side of things. When that happens, if I refresh the page, the 404 goes away and the admin page I'm trying to get to shows up.
Any leads would be appreciated.