Thanks!
Greg looks after the FTP code so, now that it looks like we know which option is causing it (at least in combination with that server and/or file), I will pass this on to him for further investigation.
If you want to provide a login for testing the site then that would be very useful. (Not sure if that's what you meant.) Best thing to do is send it via a support request to GPSoftware so that it goes straight to Greg. No need to duplicate the rest of this thread in the request; just provide a link.