The config file is writeable by the webserver. This is a major security risk because anyone can change your server settings now by using the install script.

phpBB will not be able to run until this is fixed. On unix systems this can be done with the following command:

chmod 644 config.php
Or use your FTP program to do this.
Switch on the 'read-only' attribute if you are running the script on a Windows machine.