PHP Fatal error: Class 'notifications' not found

I try Install FreePBX (http://wiki.freepbx.org/display/HTGS/Installing+FreePBX+2.11+on+Centos+6.3). But I can not to do it because i see error:

Creating or updating freepbx_conf settings…PHP Fatal error: Class ‘notifications’ not found in /var/www/html/admin/libraries/cronmanager.class.php on line 70

Can everybody help me?

so i have Centos 6 64bit, Asterisk 11 and try install FreePBX 2.11. Please help!!!