You should submit the link that is displayed when you load the sitemapindex, eg with the .gz suffix if gunzip is activated and you keep the gunzip suffix.
I've tried different settings for the root path without any luck. Right now it is this. Phpbb is installed in www.n-n-a.com/society/ :
$phpbb_root_path = './society/';
yes. the problem is already solved. it had to do with the rewrites and the advanced mod wasn't installed either. the documentation isn't very clear if you ask me, but I'm happy it's running now.