NGINX : Not possible to get rights on directories

Hi,

On ubuntu 12.04 LTS server, I've install Nginx (1.1.19 from repository ubuntu) & IspConfig following this standard documentation :
http://www.howtoforge.com/perfect-server-ubuntu-12.04-lts-nginx-bind-dovecot-ispconfig-3

Everything seems to work correctly.

After that, I've create some website with ispconfig.
Then, I've try to install some software like joomla, for example, in the website directory created by IspConfig :
/var/www/clients/client1/web1/web/

It was not possible to do that with the following rights:
sudo chown -R www-data:www-data /var/www/clients/client1/web4/web/
sudo find /var/www/clients/client1/web1/web/ -type f -exec chmod 0644 {} \;
sudo find /var/www/clients/client1/web1/web/ -type d -exec chmod 0755 {} \;

So, I've try to install with the following ones :
sudo find /var/www/clients/client1/web1/web/ -type f -exec chmod 0777 {} \;
sudo find /var/www/clients/client1/web1/web/ -type d -exec chmod 0777 {} \;

Of course, for security reasons, after installation, I've again done :
sudo chown -R www-data:www-data /var/www/clients/client1/web4/web/
sudo find /var/www/clients/client1/web1/web/ -type f -exec chmod 0644 {} \;
sudo find /var/www/clients/client1/web1/web/ -type d -exec chmod 0755 {} \;

Joomla is working.

Yet, when I try to install a component, I've an answer like :

Warning: Failed to move file!
JFolder: :files: Path is not a folder. Path: /var/www/clients/client1/web1/web/tmp/install_52d4f0bf0ec9c
JFolder: :folder: Path is not a folder. Path: /var/www/clients/client1/web1/web/tmp/install_52d4f0bf0ec9c
JFolder: :files: Path is not a folder. Path: /var/www/clients/client1/web1/web/tmp/install_52d4f0bf0ec9c
JInstaller: :Install: Cannot find Joomla XML setup file

So, there is a problem of rights (and my joomla admin panel indicate me that all my directory are unwritable)

As I've read that Nginx need to have the same rights on the master directory, I've try to apply sudo chown -R www-data:www-data /var/www/

Yet, my server provide me the following answer :

chown: changing ownership of `/var/www/clients/client1/web1': Operation not permitted

Do you have an idea ?

Thanks in advance.

Brgds

Alfred