I'm sorry that you're having trouble with the Zenfolio uploader. I wasn't able to recreate the problem that you're having.
I would like to see your Photo Mechanic log file as it may have more information about the error. Please go into Photo Mechanic's Help menu, choose "Reveal Support Data" and post the zipped log file here, PM_log.zip. Use the 'Attachments and other options' link when you're composing your reply to this message.
-Jerry