Version 2.0.3588.0 of Rebex SFTP introduced SFTP v4 support. In this version of the SFTP protocol, the layout of SSH_FXP_ATTRS message (a binary structure defined by the protocol) changed slightly to include creation time, more precision and other fields. It looks like the error reported by the server (*Unsupported operation; SSHServerAPI.SFTP.fxp_attrs*) refers to this.
This can either be a bug in Rebex SFTP or in WS_FTP Server - we will do more testing and let you know.
In either case, it should be possible to work around this issue by instructing Rebex SFTP to use SFTP v3. This should produce a behavior identical to older versions and SetFileDateTime should work:
sftp.Options |= SftpOptions.DisableSftp4;
sftp.Options = sftp.Options Or SftpOptions.DisableSftp4
sftp is an istance of