Coincidentally, I was chasing up exactly the same symptom just last week and came up with APAR PK71695...could be relevant (and has a testable workaround):
ERROR DESCRIPTION: The DATACTTIME for the FTP client is not being set properly for send processing. The result is the timer is not set and thus will never expire. ADDTIONAL SYMPTOMS: FTP client session terminate abruptly after the first EZA1485I message is issued with the following message: EZA2590E send error from send_data - EDC5120I Interrupted function call. (errno2=0x76690291). FTP Client receives EZA2590E only when TRACE is enabled. When tracing is disabled, problem does not occur. LOCAL FIX: Set DATACTTIME to 0. This disbles the data connection timer. or Set PROGRESS to 0. This disables the progress message. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html

