[WordPress] Error 404 Page Not Found When Editing Post/Page – SOLVED

Found this solution on the Wordpress.org site you need to add this line into your .htaccess file.

# BEGIN 404 Fix

< IfModule mod_env.c >
SetEnv MODSEC_ENABLE Off
PassEnv MODSEC_ENABLE
< /IfModule >

#END 404 Fix