I am facing similar issue with a slight difference. If I go to sub.domain.com/wp-admin, a 404 page is returned. Kindly suggest.
The .htaccess file is as under;
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ – [L]
# uploaded files
RewriteRule ^files/(.+) wp-includes/ms-files.php?file=$1 [L]
RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ – [L]
RewriteRule . index.php [L]
