Files uploaded, database dump not

The database dump will be stored within ‘wp-content/backups’ inside the your defined subfolder, if any, within the Dropbox app folder.

Hi Michael,
yesterday I installed your plugin and all seems working great: all files were uploaded to my Dropbox.

The database backups, instead, weren’t correctly dumped. In my Dropbox folder Apps/wpb2d/wp-content/backups I see these files:

[db-name]-plugins.sql
wpb2d-backup-log.txt

The [db-name]-core.sql is missing.

The sql file contains only some db-dump comments and these lines:

SET SQL_MODE="NO_AUTO_VALUE_ON_ZERO";
CREATE DATABASE IF NOT EXISTS [db-name];
USE [db-name];

What should I do to resolve?

P.S.
I took a look at my files and folders via FTP and the wp-content/backups folder contains only a index.php and wpb2d-backup-log.txt files.

@michael:

Oh, OK, but the Settings page says:

Please Note: Your SQL dump file will always be backed up regardless of what is selected below.

But I still need to select the (empty) folder “wp-content/backups” in order to have SQL backups?