Hi,
Can i please confirm, are you attempting to run a WordPress Multisite installation? If so continue reading, if not then please provide more information before taking the below advice.
I had the same problem today and i changed two things which fixed it. In my .htaccess file there seemed to be a small error
Firstly I set my permalinks to default, then Day and Month, and then to Post Name – this prompts WordPress to re-write the .htaccess file.
Secondly In my .htaccess file I had to change it from this:
<IfModule mod_rewrite.c>
# BEGIN WordPress
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
# add a trailing slash to /wp-admin
RewriteRule ^([_0-9a-zA-Z-]+/)?wp-admin$ $1wp-admin/ [R=301,L]
RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-(content|admin|includes).*) $2 [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(.*\.php)$ $2 [L]
RewriteRule . index.php [L]</IfModule>
# END WordPress
to this:
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
# add a trailing slash to /wp-admin
RewriteRule ^([_0-9a-zA-Z-]+/)?wp-admin$ $1wp-admin/ [R=301,L]
RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-(content|admin|includes).*) $2 [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(.*\.php)$ $2 [L]
RewriteRule . index.php [L]
</IfModule>
# END WordPress
Notice how i moved </IfModule>
down one line, and then removed the white space in-between START & END WordPress. I have no idea if this was the root cause of the problem, but it worked.