Comment: web address != to physical directory, install problem

I am commenting on an old post, but I have a problem that is somehow similar.

I installed yacs at the root of a subdomain (say subdomain.domain.com) and when I access it trough the web (typing http://subdomain.domain.com), I do get the index.php page, but without any formating. And nothing else works either.

This is because yacs is looking for the skin at "/subdomain/skins/joi/joi.css", whereas it should be looking for it in "/skins/joi/joi.css". Same with all the other files, obviously because it is the "path_to_root" that is incorrect.

I don't master all the intricacies of this, and I probably did something wrong in the installation (altough I got it right the first time, when I installed yacs in another subdomain).

My question is : can I do something (like manually alter a file ) to get everything going or do I have to reinstall ?

Thanks for your advice.