I have held the MacBook up right beside the Desktop and made sure every single setting is the same under the FTP portion.
Dropbox isn't even an option in the FTP portion of P.M., which makes it even stranger.
For a problem like this, I suggest contacting our support folks at:
By email: support@camerabits.com
By phone: +1 503.547.2800 option 2
Hours: Mon-Fri, 9:00am-5:00pm [PST/PDT]