I assume you are using the FTP Service. Which FTP client software do you use?
Anyway, since it worked before, the FTP client software is unlikely to be the problem. If you use Windows, it is recommended using DriveHQ FileManager 4.5 client software. It is fully integrated with our service. No configuration is required, and it has a lot more and better features than regular FTP.
The problem as you described seems to be related with your network connection. When it happens, please check if you can still connect www.drivehq.com, log on and download files online. If you are uploading / downloading a very large file, it's possible that the network connection could drop. You just need to retry and FTP (most FTP client software) supports resuming.