Suddenly Wordpress is acting on me and give me error 404 on all pages (but Wp-admin pages), as long as I use the document name permalink. It does work ok if I setup "simple" permalink, but obviously NOT the forum itself.

So my question is double sided: is there any way to modify the type of permalinks used by the forum (which I doubt) OR what would be the proper way to eradicate this 404 error and make Wordpress recognize my links normally again ?