Failed to load resource: the server responded with a status of 500 (Internal Server Error) - Using datatables with ajax and codeigniter

I am using datatables with ajax and jquery to get the message details from my database. when i load the file the error showing like "Failed to load resource: the server responded with a status of 500 (Internal Server Error)". Thanks in Advance.

This is My view area

<div class="row">
            <div class="col-md-4"></div> 
            <div class="col-md-4">
             <div class="panel panel-default">
               <div class="panel-heading">
                  <h3 class="panel-title">Admin</h3>
               </div>
               <div class="panel-body">
               <form action="" method="post" id="frm_login">
               <div class="form-group">
                  <label for="adminname">Admin Name</label>
                  <input type="text" class="form-control" name="adminname" id="adminname" placeholder="Admin Name" required="required">
                </div>
                <div class="form-group">
                  <label for="adminpassword">Password</label>
                  <input type="password" class="form-control" name="adminpassword" id="adminpassword" placeholder="Password" required="required">
                 </div>
               <button type="submit" class="btn btn-primary" id="submit">Submit</button>
              </form>
                </div>
              </div>
            </div> 
            <div class="col-md-4 "></div> 
        </div>
    </div>      

This is my Ajax and datatable area

<script src="<?php echo base_url("assets/js/jquery-1.12.4.min.js");?>"></script>
            <script src="<?php echo base_url("assets/js/bootstrap.min.js");?>"></script>
            <script src="http://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
            <script src="https://cdn.datatables.net/1.10.13/js/jquery.dataTables.min.js"></script>
            <script>
                var table;
                table=$('#messages').DataTable({
                   "ajax":{
                     "url":"<?php echo base_url("Admin_Creator/viewmessage") ?>",
                     "type":"post"
                   }
                });

             });
           </script> 

This is my Controller area

        public function viewmessage(){  
              $show=$this->Model_Creator->Select_Message();
              $data=array();
              foreach($show as $rows){
                  array_push($data,
                          array(
                          $rows['message']
                          )
              );
           }
           $this->output->set_content_type('application/json')->set_output(json_encode(array('data'=>$data)));    
        }

This is my model area

       public function Select_Message(){  
             $this->db->select('*');
             $this->db->select('messages');
             $query=$this->db->get();
             return $query->result_array();
           }

Try as below...load url helper in your controller's __construct() function.

Controller:

public function viewmessage(){  
              $show=$this->Model_Creator->Select_Message();
              $data=array();

              foreach($show as $rows){
                  array_push($data,$rows['message']);
              )
           }
           $this->output->set_content_type('application/json')->set_output(json_encode(array('data'=>$data)));    
        }

Model

public function Select_Message(){ 

     $this->db->select('*');
     $this->db->from('messages');
     $query=$this->db->get();
     return $query->result_array();
   }