Cannot delete object: E/Delete Error﹕ object not found for delete

public class PostThreadActivity extends ListActivity {

    private SwipeRefreshLayout mSwipeRefreshLayout;
    private ParseQueryAdapter<Comment> mainCommentAdapter;
    private CommentAdapter favoriteCommentAdapter;
    protected List<ParseObject> mComments; //create this member variable in order be able to delete comments

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.post_thread_layout);
        getListView().setClickable(true);

        Intent i = getIntent();
        //Get the result of
        String title = i.getStringExtra("title");
        String location = i.getStringExtra("location");
        String description = i.getStringExtra("description");
        String rating = i.getStringExtra("ratings");
        //String photo = i.getStringExtra("photo");

        //TextViews of the singleItems
        TextView titleTextView = (TextView) findViewById(R.id.title);  //Get the textView for the title from item_list_favorites.xml and convert it to a variable titleTextView. Then gets the submitted Event title info from getters and setters: getTitle, then set it as text of TitleTextView //simple.
        titleTextView.setText(title);
        TextView locationTextView = (TextView) findViewById(R.id.location);
        locationTextView.setText(location);
        TextView descriptionTextView = (TextView) findViewById(R.id.description);
        descriptionTextView.setText(description);
        TextView ratingTextView = (TextView) findViewById(R.id.rating);
        ratingTextView.setText(rating);


        /*ParseImageView mealImage = (ParseImageView) findViewById(R.id.icon_in_post);

        ParseFile photoFile = meal.getParseFile();
        if (photoFile != null) {
            mealImage.setParseFile(photoFile);
            mealImage.loadInBackground(new GetDataCallback() {
                @Override
                public void done(byte[] data, ParseException e) {
                    // nothing to do
                }
            });
        }
        */


        mSwipeRefreshLayout = (SwipeRefreshLayout) findViewById(R.id.activity_main_swipe_refresh_layout);

        mainCommentAdapter = new ParseQueryAdapter<Comment>(this, Comment.class);
        mainCommentAdapter.setTextKey("commentText");
        //mainCommentAdapter.setImageKey("photo");

        favoriteCommentAdapter = new CommentAdapter(this);

        // Default view is all comments
        final ListView commentsListView = (ListView) findViewById(android.R.id.list);
        commentsListView.setAdapter(mainCommentAdapter);


        //adapt to show favorites adapter view
        showFavoritesComments();

        getListView().setOnItemClickListener(new AdapterView.OnItemClickListener() {
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                final Comment item = favoriteCommentAdapter.getItem(position);

                Toast.makeText(getApplicationContext(),
                        "Click ListItem Number " + position, Toast.LENGTH_LONG)
                        .show();


                AlertDialog.Builder builder = new AlertDialog.Builder(PostThreadActivity.this);
                builder.setTitle("DELETE COMMENT");
                builder.setMessage("Are you sure you want to delete this comment?");
                builder.setPositiveButton("YES", new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int which) {
                        // Delete the comment
                        item.deleteInBackground(new DeleteCallback() {
                            @Override
                            public void done(ParseException e) {
                                Log.e("Delete Error", e.getMessage());
                            }
                        });
                        dialog.dismiss();
                    }
                });

                builder.setNegativeButton("NO", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        // Do nothing
                        dialog.dismiss();
                    }
                });
                AlertDialog alert = builder.create();
                alert.show();
            }
        });