Message EZA1777I is displayed

The FTP client displays the EZA1777I subcommand fails: the target generation data set cannot be a library message. This message is issued when the MVSGet or MVSPut subcommand is transferring a library into a generation data set. But the generation data sets cannot be PDSEs, UNIX files, or VSAM data sets. See z/OS DFSMS Using Data Sets for information about Processing Generation Data Groups.