This error usually results into a plain white screen
with no error message. This makes it the most
puzzling because you have no clue where to look and
what to fix.
Most of the time it is caused when a script exhausts
PHP memory limit. It can also happen due to a
configuration on the server. It is also possible that a
user would only see white screen of death on certain
sections of their site.What you need to do is fix your
permalinks settings.
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 fixes the
WordPress posts 404 error. However, if it does not
work for you, then you probably need to update your
.htaccess file manually.
Login to your server using FTP, and modify the
.htaccess file which is located in the same location
where folders like /wp-content/ and /wp-includes/ are
located. The easiest thing you can do is to temporarily
make the file writeable by changing the permissions
to 666. Then repeat the original solution. Don’t forget
to change the permissions back to 660. You can also
manually add this code in your .htaccess file:
How To Fix Wordpress Posts Returning 404 Error