The LIST or NLST command requested members of a PDS, but the FTP server was unable to open the PDS to read the directory. This can be a temporary problem, for example the data set is currently in use, or it can be a permanent error with the data set.
The LIST or NLST command is rejected.
Reissue the command. If the problem persists, contact the system programmer for the server system.
Correct the problem with the data set.