I have a root site, (root site collection), I created a sub site with break inheritance from root site (remove inheritance). I gave user1 permission to the sub site, but he has no permissions on root site. when he browses to sub site he gets Access Denied. I don't know why. I used a module to provision my images and css files on root web which the sub site uses as well (same master page). can it be because of that? how can i fix this problem? thank you.
Maybe, check the user has permissions to master page, CSS and images. If we didn't had permission on those files, we always get the AccessDenied.
In such cases, it's always better to put your Images, CSS etcs in the Master Page Gallery (_catalogs/masterpage). Even anonymous users have permission to the files stored here so you wont have any permission issues accessing this gallery from a sub site with broken inheritance.