The problem is probably involved with perms.
You can try this actions:
* Check that www-data user is on sudoers with no password. You should write a line like this at the end of your sudoers file (with visudo command of course)
To check that www-data is on sudoers just as root execute
sudo ls -la
If no password is required and the output of ls -la is shown, www-data can execute commands with sudo.
* Check that www-data is the owner of /var/www/meshlium (or the path of your manager system folder) to do that simply execute as root:
chown -R www-data:www-data /var/www/meshlium
chmod -R ug+w /var/www/meshlium
After this steps manager system should be able to write files. But if you continue with problems we can try some more checks.