Updating from CI 1.7.2 to CI 2.0.0 - class CI_Controller not found

[eluser]peekk[/eluser]
Hello, i;m trying to update my old version of codeigniter platform, and path to my CI is:
/home/user/www/mysite. That's all right, it's written here: http://ellislab.com/codeigniter/user-gui...e_200.html That I should replace my system folder (except application folder) with this from 2.0 (i want to update to 2.0).

I copied these directories from 2.0.0's system folder (that's core, database, fonts, helpers, language, libraries) and replaced them with these from 1.7.2. I've done all other things - and after trying to launch my new version of CI - it shows Fatal error: Class 'CI_Controller' not found in /home/user/sitesystem/application/controllers/ctrl1a.php on line 3.

MY /system/core folder contains file Controller.php and it starts with

Code:

class CI_Controller

- so everything should work fine - what's going on?