Please see a response here:
https://ww.wp.xz.cn/support/topic/i-want-to-use-a-different-background-on-sub-pages-how?replies=2
And, please only post your question once after you please review how to post and how best to get help in this forum:
http://codex.ww.wp.xz.cn/Forum_Welcome
Here is what is happening:
One site has a server level 404 set up. Ask the host of that site about it. The second does not and uses the theme’s 404.php file.
Of course, it may also help to review if both site’s themes have a 404.php. Review theme files, or ask theme providers.
That second post was meant for another thread! The first one applies.
