Occasionally, you’ll find this error is that when a user visits a single post on their site they get a 404 page – not found error. But you can still browse all other sections of their site including the admin area.

Alright now, you will have to remember which post or page that you might have deleted (and have not deleted the link). Or most probably you have not change the link after you change it.

If that does not solve your problem. Login to your wp-admin and go to Settings » Permalinks, and simply click on Save Changes button. This will update your permalinks settings and flush rewrite rules. In most cases this solution will fix the WordPress posts 404 error.

If this still does not solve your problem, then you will need to update your htaccess file manually. Login to your server using FTP, and find the .htaccess file. It is located in the same location where folders like /wp-content/ and /wp-includes/ are located.

Inside the htaccess file, insert the following:-

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ – [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress