This could be related to an outdated library or invalid login credentials. The login method takes appKey, username, appliaction name, password as the parameters.
Using the same calls as above with the latest library retrieved from rubyforge I get:
irb(main):010:0> root_folder = session.GetRootFolder(1, 500, 0, true)
=> #<NVX::SDS::Folder:0x31b85e8 @fs_folder_list=#<NVX::SDS::FSFolderList:0x2e05a
e0 @file_attributes=[#<NVX::SDS::FSFileAttributes:0x2e54564 @created_date="Sun, ... (quite a bit more as well)
Let me know if you have the latest version and have verified your login credentials using:
http://services.nirvanix.com/ws/authentication/Login.ashx?appKey=XXXX&username=XXXX&password=XXXX
Regards,
Barry R.