how can i fix it ?

remzi

Fatal error: Call to undefined function IsWritable() in /home/tepeduyu/public_html/library/core/class.filesystem.php on line 271

peregrine

what version of vanilla?

also you might reload core files.

also check

http://vanillaforums.org/discussion/20231/how-to-become-somewhat-adept-at-modifying-vanilla-to-meet-your-needs-for-free