Snapshot Dropbox 'Fail'

Hi, the Snapshot plugin I bought earlier this week is 'failing' to export to Dropbox.

I've added/removed Dropbox several times (tried it with different Dropbox accounts - all paid ones) but it's still says "Fail". However, it backs up to the local server fine when I change the options from Dropbox to the web server.

I've enabled admin support on the site in question kevreilly.com

Thanks