i etracted the oxwall software in side a file called community which site inside the root directory
So the url would be www.maindomain.com/community right?
define('OW_URL_HOME', 'http://www.example.com/');
to
define('OW_URL_HOME', 'http://www.example.com/community/');
dont forget the trailing / it must have one.
i already know the answer to that, no you didnt did you :)..
remove that line of code you added and run the install please...
here is your reference
https://wiki.oxwall.com/install:manual_installation
Dave ;)