problem installing on localhost (I am a php ignorant)

Hi there,
I just aquired and downloaded Datatables and Editor.
I try to install them on my local ubuntu box.
To do so I created a mysql database with the sample data I found (mysql.sql, and data.sql).
In /var/www/DataTables
I installed /DataTables-1.9.4 and unziped Editor in its extras directory.

Now when I try to access one of the samples in /var/www/DataTables/extras/Editor-1.2.4/examples
I get an error:
DataTables warning (table id = 'example'): DataTables warning: JSON data from server could not be parsed. This is caused by a JSON formatting error.

and in firebug the following console get message is provided:
<br />
<b>Fatal error</b>: Call to undefined function DataTables\Database\json_encode() in <b>/home/zope/key2go/datatables/DataTables-1.9.4/extras/Editor-1.2.4/examples/php/lib/Database/Driver/Mysql/Query.php</b> on line <b>55</b><br />

Now my question:
How can I debug this?
My problem is, I have NO idea about php (I only want to use php for the samples)
Tell me please if you need more infoormation about my setup.

thanks for your time
robert