What is "Windows FTP Client"? You should not use Windows Command-line FTP as it only supports Active FTP, which is usually blocked by firewalls.
You can use Internet Explorer connecting to:
ftp://USERNAME:PASSWORD@ftp.drivehq.com/
It is recommended using DriveHQ FileManager or any third party FTP client software. FileManager is strongly recommended as it also has a lot more features (such as Folder Synchronization, Sharing and Publishing, etc) and is native to DriveHQ service.
