I've just installed this plugin and all appears to be working other than the important part of uploading the zipped (I have paid for the extension) backup file to Dropbox.
Can confirm that 'Wordpress Backup to Dropbox' is showing in 'My apps' for my Dropbox account.
The plugin has been deleted and reinstalled.
Looking at the 'Backup Log' I can see the upload process starting but that's were it stops (I have left it running overnight) and the zip file is 34MB in size.
Looking for advice, thanks in advance.