generated download not working for me

i do the same as described here

http://editor.datatables.net/manual/generator

but i get this error.

DataTables warning: table id=todo - Invalid JSON response. For more information about this error, please see http://datatables.net/tn/1

any idea what to do?

also when i add the data gives me this error

"A system error has occurred"

what to do now?

i am using in localhost + wamp server + windows