Matomo and Zend_Session require the session extension
It appears your PHP was compiled with
--disable-session. To enjoy Matomo, you need PHP compiled without that configure option.
Matomo requires the php5-json extension which provides the functions
It appears your PHP has not yet installed the php5-json extension.
To use Matomo, please ask your web host to install php5-json or install it yourself, for example on debian system:
sudo apt-get install php5-json.
Then restart your webserver and refresh this page.