Integrates DropBox with your blog allowing you to post images and files directly from your DropBox. Requires PHP 5.2 and cURL.
Common problems are you don't have cURL support or that your server time is incorrect. Check with your host to verify these possibilities.
Yes, you need an account with DropBox to use this plugin.
There is not much to be done about this except ask your provider to update. The plugin will check for requirements on activation and let you know if something is missing.