Go to the FTP Traces page for information on collecting a client trace. A trace with options FLO, SOC, FSC, INT, TIMESTAMP, and UTL will be needed. The trace should be activated at startup using the FTP.DATA DEBUG statements.
In addition to the client debug trace, a packet (SYSTCPDA) trace should be obtained in the event that the network interaction (on either the control or the data connection) need to be analyzed. Information on packet tracing can be found in Informational APAR II12014. Note that the client trace and the packet trace should be taken concurrently. This will ensure that the two traces contain the same instance of the error, and can therefore be compared appropriately.
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.