I think the problem is that you are entering information for the domain and username. Follow me on this one. When you FTP to your account, you will automaticly be in:
So if you tell your FTP program to send you to /username/domain then you are trying to go to:
Try not giving it any folder information and see what it does.
Additionaly, there is a Web FTP client built into the Control Panel. Go to Manage Users and click something like Log In next to your name. That will bring you to the base dirrectory for that user. If it is you, this will be your home dirrectory.
Now dont fall in love with that Web FTP client, but it will let you see your structure and upload relativly small files.