Reply To: 503 error on reply page of wp-admin
This probably comes too late to be of any use to you, and maybe your error had a different cause, but I encountered this problem on my site yesterday and was able to fix it by deleting some replies that did not have associated parent topics in the wp_posts database.
I accessed wp_posts using PHP My Admin, entered “reply” next to “post type”, and manually deleted all posts that had “0” under their “Post parent”.
In my case the error appeared after I clicked on “Replies” – “Add new” – “Preview” in the dashboard. It created an errant entry in the database. It’s probably a bbPress bug.
Please use maximum caution before modifying the database though, and don’t do it if you don’t have a proper backup.
