Some servers return messages like "500 User Exit denies Userid 'YYYYYYY' from using Command 'NOOP'.", which renders the validateObject method above unusable (always returns false)
Example FileZilla log from a very restrictive FTP server setup:
Status: Connecting to XXX.XXX.XX.XX:21...
Status: Connection established, waiting for welcome message...
Response: 220-FTPD1 IBM FTP CS V1R12 at XYZ.COM, 14:17:26 on 2012-01-13.
Response: 220 Connection will close if idle for more than 5 minutes.
Command: USER YYYYYY
Response: 331 Send password please.
Command: PASS ******
Response: 230 YYYYYY is logged on. Working directory is "/XXXX/YYYY".
Response: 215 UNIX is the operating system of this server. FTP Server is running on z/OS.
Response: 500 User Exit denies Userid 'YYYYYY' from using Command 'FEAT'.
Maybe a solution could be to try to resend login credentials (or some other "dummy" command) in case sendNoop() returns false but no exception is thrown?