snapshot not backing up, no files processed


I'm running Snapshot on several sites. Backups are sent to Dropbox.

On this site I have a snapshot entry for a weekly backup. However the backup is not processed and no files are stored in Dropbox. When I click run now it says creating archive but nothing happens. This did work in the past and as far as I can recall nothing has changed on this site. On other sites with the same settings it works fine.

Please assist.