I just install zabbix from official rpm and try to convert to multi node

1. /usr/sbin/zabbix_server -n 2 -c /etc/zabbix/zabbix_server.conf
   Dropping foreign keys ....................................................................................................................................... done.
   Converting tables ............................................................................................................ done.
   Creating foreign keys .................................................................................................................................zabbix_server [3254]: Error: [Z3005] query failed: [1452] Cannot add or update a child row: a foreign key constraint fails (`zabbix`.<result 2 when explaining filename '#sql-79c_19118'>, CONSTRAINT `c_sessions_1` FOREIGN KEY (`userid`) REFERENCES `users` (`userid`) ON DELETE CASCADE) [ALTER TABLE `sessions` ADD CONSTRAINT `c_sessions_1` FOREIGN KEY (`userid`) REFERENCES `users` (`userid`) ON DELETE CASCADE]
   ......Conversion failed.

Centos

1. cat /etc/centos-release
   CentOS release 6.2 (Final)

Mysql & Zabbix 2.2.1

1. rpm -qa |grep mysql
   mysql-server-5.1.69-1.el6_4.x86_64
   zabbix-server-mysql-2.2.1-1.el6.x86_64
   php-mysql-5.3.3-23.el6_4.x86_64
   mysql-libs-5.1.69-1.el6_4.x86_64
   zabbix-web-mysql-2.2.1-1.el6.noarch
   mysql-5.1.69-1.el6_4.x86_64