JQuery.Ajax giving trouble in inserting data

I want to save data from Textbox on Button click. I am using JQuery AJAX for this task like below. Please note that I made this tags inside theme function.

   function theme_user_post_block($vars)
  {
    $themeUserCommentInput ='';

    $themeUserCommentInput .= '<textarea id="txt_1" rows="1" cols="50"></textarea>';

    $themeUserCommentInput .= '<input type="submit" value="Post Comment" align="center"
    class="btnPostComment" id="btn_1" />
    return $themeUserCommentInput;
  }

This able to show me Textbox and Button inside the page. Now here is my JS code:-

   (function($) 
   {   
    Drupal.behaviors.PostComment= { 
 
     attach: function (context, settings) {
      $('.btnPostComment', context).click(function (event) {
      var post = "&newcomment=Comment1&logid=log1";
      jQuery.ajax({
                  url: 'postcomment',
                  type: 'POST',
                  dataType: 'json',
                  data: post,
                  success: function (data) { alert(data); },
                  error: function(jqXHR, textStatus, errorThrown) {alert(textStatus + errorThrown);}
          });               
         });
        }                    
       }
      })(jQuery); 

Next I create a Menu Page with URL Name as follows:-

     function postcomment_menu(){
     $items=array();
     $items['postcomment']=array(
       'title'=>t(''),
       'type'=> MENU_CALLBACK,       
       'page callback' => 'user_comment_post',        
       'access arguments' => array('access content'),
     );
     return $items; 
    }

    function user_comment_post(){
    global $user;
     $cid =  db_insert('user_comment')
		->fields(array(		
		'comment_user_id' => $user->uid,
		'reference_id' => $_POST['logid'],		
		'comment_desc'=>$_POST['newcomment'],
		'createdon'=>REQUEST_TIME, 
		))
		->execute();
      if($cid!=0)
      {
         //GetUserComments($i);
         drupal_json_output("success");
      }
    }

So I have done all things that is required for jQuery+Ajax Submit functionality. When I press
"Post Comment" button it gives me error in alert says "errorundefined". The alert shows as a
result of error inside the jQuery.AJAX function. Also the custom menu callback is also not getting
called.