Trouble redirecting to a subfolder

I’ve setup my multisite in a subfolder and done as recommended in adding the folder name to the wp-config.php file and copied it to the root and I’ve made the changes to the htaccess file.

Unfortunately when I now try to access domain.com I get left with “Error establishing a database connection”. Clearly I’ve missed something in one of those files as the site still works fine if I go to domain.com/subfolder but whatever I’ve missed, I can’t find it.

Help?