I know this is kinda old, but I want to make sure others that run into this problem can find a solution: 

From: http://support.ajenti.org/topics/1122-installing-on-centosrhel/

Ajenti requires EPEL repositories: http://fedoraproject.org/wiki/EPEL

Add repository key:

wget http://repo.ajenti.org/ajenti-repo-1.0-1.noarch.rpm 
rpm -i ajenti-repo-1.0-1.noarch.rpm