Since you receive "connected" it means you have the FTP server running on the AS/400.
Try to look in the FTP server jobs joblog, the job name is qtftpxxxxx in subsystem qsyswrk.
You can also perform some debug functions on the AS/400 this way:
* netstat and choose option 3
* Find the connection between your machine and the
AS/400 over the FTP port (21), and choose option 5.
This was first published in April 2001