New Multisite, 404 errors

I have been working on this, off and on, for a week. I have found lots of comments about problems with the .htaccess file but that doesn’t seem to be the issue – it, and the config files, all look correct.

This is a new install, now tried on two separate servers, each resulting in the same problem – I can create the main site, but when I create the first subdirectory site, I get 404 errors when trying to access it.

Have checked the .htaccess and wp-config files many times and they all match – is there something else I need to look at?

.htaccess here:

RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ – [L]

# uploaded files
RewriteRule ^([_0-9a-zA-Z-]+/)?files/(.+) wp-includes/ms-files.php?file=$2 [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).*) $1 [L]
RewriteRule ^[_0-9a-zA-Z-]+/(.*\.php)$ $1 [L]
RewriteRule . index.php [L]

Thoughts? Incantations? Do I need to find an aging chicken …?

Thanks.