ajax中的服务器错误500

I am working with codeigniter.I have a controller called "User" and in that controller i have a method called "apply" which is bound to a form .With my ajax i am trying to implement a post request but in return i get internal server error 500 error .How i can fix this.I have my index.php page removed by an .htaccess file

 $.ajax({
       url:'http://localhost/mycodeigniter/ci/user/apply',
       type:'POST',
       data:{
           start:'3/3/2012',
           end  :'4/3/2012',
           reason:'sick'
           },
       success: function( data, textStatus, jQxhr ){
                    alert( data );
                },
        error: function( jqXhr, textStatus, errorThrown ){
                     alert( 'baler '+errorThrown );
                }
   });

Try access vía url to method:

http://localhost/mycodeigniter/ci/user/apply

Or try http://localhost/mycodeigniter/index.php/ci/user/appl

Since you're not using HMVC, you should typically access your controller's methods like this:
your-local-project-path/controller-name/method-name

So, the above request should work at following URL http://localhost/mycodeigniter/user/apply

This may help you

 /*
     |my sql date formate is 2012-3-4
     |and if not then first check your date in mysql and change your date according to this "date()" method    |used below
     */

    public function get_detail()
    {
        $start = $this->input->post('start');
        $end = $this->input->post('end');
        $reason = $this->input->post('reason');
        $start_date = date('Y-m-d',$start);
        $end_date = date('Y-m-d',$end);

        /*Pass data in model through function */

        $data = $this->model_name->function_name($start_date,$end_date,$reason);

    }