In FTP adapter, when there is an error excluding the network failure during the file update when update process is started, error details are displayed in the log as log level "WARN" and the subsequent process is continued.
The reason for the above behaviour is that you can upload multiple files at the same time in FTP update process which in turn performs the subsequent file transfer even if there is a file transfer failure.
When you want to make the script execution itself error during permission error then, "NG" should be set in the "Status" attribute of the file wherein the error occurred, therefore by determining that value in the conditional branch process you can handle the error.