Created Unassigned: Getting File Not Found on all Upload/Delete/... cmds on my target file. [1699]

Downloaded SFTP app [ Renci.SshNet ] from "codeplex" .
Cannot get

sftp.BeginUploadFile( streamparm, targetfilepath)
or
sftp.UploadFile ( streamparm, targetfilepath, null )

to work.

Keep getting "File Not Found" error.

streamparm was created by :
System.IO.Stream streamparm = System.IO.OpenRead("c:\temp\test.csv");

I tried:
string targetfilepath = "sftp://sftp.dfs.com/sfd/test.csv";
string targetfilepath = "sftp.dfs.com/sfd/test.csv";
string targetfilepath = "sfd/test.csv";

sftp.ChangeDirectory("sfd");
string targetfilepath = "test.csv";

nothing works. Need help.

[ NOTE: sftp.ChangeDirectory("sfd"); . . . and . . . sftp.Create("sfd/test.csv"); . . . works ]