Thanks for your reply. We are using version 5.1.4 and I believe this is likely causing the issue. After looking through the version history, it seems that TIMESTAMP is not available in our version and that we will need to upgrade. I will try upgrading and then see if my code works.
Please attach a full session log file showing the problem (using the latest version of WinSCP).
To generate the session log file, use
/log=path_to_log_filecommand-line argument. Submit the log with your post as an attachment. Note that passwords and passphrases not stored in the log. You may want to remove other data you consider sensitive though, such as host names, IP addresses, account names or file names (unless they are relevant to the problem). If you do not want to post the log publicly, you can mark the attachment as private.