AliG1000 on "404 error where a page does exist"

I am using WPML. I have a Spanish version of a home page at domain.com/es When I edit the page, I can see that there is content and I can preview it. However, when I try to view it at domain.com/es I get a 404 error.

The .htaccess appears to be standard and it starts off like this:

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress

It was all working, and now it's not. I can't for the life of me work out why.