WPMU Problem to get Admin over SSL

I’m using WPMU 3.0RC2 and want to get wp-admin secured.

Using the subdir setup
http://www.domain.com/site1/
http://www.domain.com/site2/
http://www.domain.com/site3/
…

I’ve added 2 lines in wp-config.php
define(‘FORCE_SSL_LOGIN’, true);
define(‘FORCE_SSL_ADMIN’, true);

When I go to http://www.domain.com/site1/wp-admin/ it redirects to https://www.domain.com/site1/wp-admin/ which is correct but gives me a 404

Do I need to add something special rules to my VirtualHost or .htaccess to get this to work?

Thanks