MyBB Hacks

Hello.
Well I got all the files to the root of my forum and when I go to plugins i get this error:

Warning [2] require(/var/www/inc/xthreads/xt_admin.php): failed to open stream: Permission denied - Line: 99 - File: inc/plugins/xthreads.php PHP 5.3.6-13ubuntu3.3 (Linux)

/inc/plugins/xthreads.php                 99 errorHandler->error
/inc/plugins/xthreads.php                 99 require
/admin/modules/config/plugins.php 477 require_once
/admin/index.php                         517 require

My MyBB version is 1.6.5
Thanks
PD : Sorry for my English i'm Spanish.

Solucioned (Y) I'm actualized Mybb

Make sure you've uploaded everything correctly.
In particular, make sure you haven't randomly removed permissions from files.