I know that this post is 4 years oldie, but i think my answer will help more than one user 
In my case the problem was that i had changed the permissions to access the file conf/conf.php so restrictive that it caused the same Dolibarr not able to access its content, and then it tried again and again to install itself.
In my case i setted chmod 700 to that file, but i needed to assign 644 to be able to “apache user” to read the content.
