CodeIgniter + jQuery UI autocomplete = 500 internal server error (with code) due to CSRF set to TRUE

This is almost certainly a CSRF token issue.

See this in the CI forums and this blog post

Nothing in your question suggests that you need to turn query_strings on or allow_get_array

Try this

comment out this line

$search = $this->input->post('term');

then add $search to your function as the first argument

public function ac2($search)

Then just try to hit the URL with a browser

http://yourdomain.com/index.php/test/ac2/<insert your search string here>

Now that we know your url is good

change your controller back.

try this...

data: 'term='+req,  //<-- change to this

seems you are missing sendig the csrf token with the POST data, try:

    $("#input").autocomplete({        source: function(req, add){    var cct = $("input[name=ci_csrf_token]").val(); //  <---            $.ajax({                url: '<?php echo base_url(); ?>test/ac2',                dataType: 'json',                type: 'POST',                //data: req,                data: 'input='+req,    'ci_csrf_token': cct,   //  <---                success: function(data){                    if(data.response =='true'){                       add(data.message);                    }                }            });    },    minLength: 2,    select: function(event, ui){        $(this).end().val(ui.item.value);        }    }); }); 

you can also find the token like:

     csrf_test_name:$("input[name=csrf_test_name]").val(),

that token is generated in the view when using the form helper and opening it like:

  <?php echo form_open();?>

sources: * http://codeigniter.com/forums/viewthread/176318/** own headache