Your comments

Which python-gevent-socketio version is installed?
Sorry, I missed that. However there's a "custom top-level configuration" field, whose content goes into NGINX's http {} block and applies to everything.
You should be able to override global client_max_body_size through Websites > Advanced > Custom configuration.
You only need to replace the postmaster email (or remove it completely). 
x._domainkey is used as-is.
Do you have any caching proxies between you and the internet?

CentOS 6.5:

Downloading Packages:
ajenti-v-mysql-0.3.1-1.noarch.rpm | 5.4 kB 00:00
Running rpm_check_debug
Running Transaction Test
Transaction Test Succeeded
Running Transaction
Installing : ajenti-v-mysql-0.3.1-1.noarch 1/1
Verifying : ajenti-v-mysql-0.3.1-1.noarch 1/1


Installed:
ajenti-v-mysql.noarch 0:0.3.1-1


Complete!

yum clean all and try again (see Troubleshooting on the install page).
I've updated the python-gevent-socketio package, please reinstall again.
Ajenti V works with any modern Nginx versions, starting from 1.0.0
Hi Aminul,

.htaccess is an outdated technology (in fact used almost only with PHP), and isn't supported by NGINX. But you can convert your .htaccess rules into NGINX custom configuration here: http://winginx.com/en/htaccess
Is this the amount taken by Ajenti, or by the system in whole?