Are you using CentOS 7 / RHEL 7?

If you install it successfully, ajenti-panel -v should be working.

Sorry, but what does "inconnue" mean? If it's "not found", then you didn't install Ajenti. Try running the quick-installer script again and looking for any hints in the output.

Try stopping ajenti, and then running: ajenti-panel -v in your terminal. This should give you something for diagnostics. If it starts successfully, then try opening the panel through browser.

This is likely caused by half-installed PIP packages :/
Try: pip uninstall python-ldap

Check it by running ajenti-panel -v

If you need to manipulate data in the tables (and you don't know SQL), you need to use a more dedicated tool, such as phpMyAdmin. Installing pMA on Ajenti V: http://support.ajenti.org/topic/479448-installing-phpmyadmin/

One of these should work for you:

CentOS 6	ftp5.gwdg.de/pub/opensuse/repositories/server:/mail/CentOS_6/x86_64/python-lxml-2.3.3-20.1.x86_64.rpm
CentOS 6	ftp5.gwdg.de/pub/opensuse/repositories/server:/mail/CentOS_6/i386/python-lxml-2.3.3-20.1.i386.rpm

On a side note, configuring CSF is a much more realistic option in this case.

What happens if you try to install python-lxml directly?