Snapshot not working since I updated it

Snapshot was working great, but it's no longer working. It gets all the way to the last step and then says "An unknown error occurred." This is true only for one of my sites. I have others, running on the same server, where Snapshot is working fine. The problem seems to have originated when I updated Snapshot to the latest version. Note that I'm running WP 3.6.1. Thanks!