DokuWiki uses ordinary files for the storage of wiki pages and other information associated with those pages (e.g. images, search indexes, old revisions, etc). In order to operate successfully DokuWiki must have write access to the directories that hold those files. This installer is not capable of setting up directory permissions. That normally needs to be done directly on a command shell or if you are using hosting, through FTP or your hosting control panel (e.g. cPanel).
This installer will setup your DokuWiki configuration for ACL, which in turn allows administrator login and access to DokuWiki's admin menu for installing plugins, managing users, managing access to wiki pages and alteration of configuration settings. It isn't required for DokuWiki to operate, however it will make Dokuwiki easier to administer.
For security reasons this script will only work with a new and unmodified Dokuwiki installation. You should either re-extract the files from the downloaded package or consult the complete Dokuwiki installation instructions