error: cannot access Task

@Override
    protected void onResume() {
        super.onResume();

        mCurrentUser = ParseUser.getCurrentUser();
        mFriendsRelation = mCurrentUser.getRelation(ParseConstants.KEY_FRIENDS_RELATION);

        setProgressBarIndeterminateVisibility(true);

        ParseQuery<ParseUser> query = ParseUser.getQuery();
        query.orderByAscending(ParseConstants.KEY_USERNAME);
        query.setLimit(1000);
        query.findInBackground(new FindCallback<ParseUser>() {
            @Override
            public void done(List<ParseUser> users, ParseException e) {
                setProgressBarIndeterminateVisibility(false);

                if (e == null) {
                    //Success
                    mUsers = users;
                    String[] usernames = new String[mUsers.size()];
                    int i = 0;
                    for (ParseUser user : mUsers) {
                        usernames[i] = user.getUsername();
                        i++;
                    }

                    ArrayAdapter<String> adapter = new ArrayAdapter<String>(
                            EditFriendsActivity.this,
                            android.R.layout.simple_list_item_checked,
                            usernames);
                    setListAdapter(adapter);

                    addFriendCheckmarks();
                } else {
                    Log.e(TAG, e.getMessage());
                    AlertDialog.Builder builder = new AlertDialog.Builder(EditFriendsActivity.this);
                    builder.setMessage(e.getMessage())
                            .setTitle(R.string.error_title)
                            .setPositiveButton(android.R.string.ok, null);
                    AlertDialog dialog = builder.create();
                    dialog.show();
                }
            }
        });
    }