Go to the FTP Traces page for information on collecting a client trace. A trace with options FLO, INT, ACC, and SOC(3) will be needed. The trace should be activated via DEBUG statements in the FTP.DATA file.
If this client is using SSL, SEC should also be added to the list of FTP debug options. Additionally, a system SSL trace may be needed. Instructions on gathering this trace can be found on the FTP server and client SSL Diagnostics and Common Problems page.