bServerSide issue when set to true

I took the php script from the example page in the datatables site and modified it to my needs. I've already verified the json at jsonlint.com to be valid. With bServerSide being false everything went okay, but when I turn it to true, the loading went forever whilst chrome reported there's a json error. I wonder what have I been missing .. the following is the link the datatables live:

http://live.datatables.net/usoruf/3/edit

Thank y