Hi have ProFTPD runningon a brand new CentOS 5.8 server with Plesk, and its behaviour is inconsistent at best. I tried to transfer a directory from my PC, and every time I get a transfer failed on a random file. It's never the same one that fails, it just fails. Sometimes it's a .gif, sometimes it's a .css, sometimes it's a JPG. Of several hundred files, a dozen is always failing for no apparent reason.

The error that I get is the following:

COMMAND:>   [27/11/2012 11:43:52] STOR main_border.gif
        [27/11/2012 11:43:53] 500 Invalid command: try being more creative
ERROR:>     [27/11/2012 11:43:53] Syntax error: command unrecognized.

The above is just an example, the "command unrecognized" occurs with LIST and other commands as well.

Here's the ProFTPD configuration, just in case:

ServerName                      "ProFTPD"
#ServerType                     standalone
ServerType                      inetd
DefaultServer                   on
<Global>
DefaultRoot     ~               psacln
AllowOverwrite          on
</Global>
DefaultTransferMode     binary
UseFtpUsers                     on

TimesGMT                        off
SetEnv TZ :/etc/localtime
Port                            21
Umask                           022

MaxInstances                    30

ScoreboardFile /var/run/proftpd/scoreboard

TransferLog /usr/local/psa/var/log/xferlog

#Change default group for new files and directories in vhosts dir to psacln

<Directory /var/www/vhosts>
        GroupOwner      psacln
</Directory>

# Enable PAM authentication
AuthPAM on
AuthPAMConfig proftpd

IdentLookups off
UseReverseDNS off

AuthGroupFile   /etc/group

Include /etc/proftpd.include

Note: file /etc/proftpd.include is blank.

The above is the default configuration set by Plesk 11. I don't know much of why is that way, my knowledge of Linux System Administration is very basic and the one of ProFTPD is a complete zero.

Thanks in advance for the help.

Update
Issue experienced with CuteFTP and FileZilla.

Update
Replaced ProFTPd with PureFTPd, issue persists. Sometimes I get "command unrecognized", sometimes "failed to establish data connection". I'm starting to think that it could be a network issue, but I have completely zero knowledge of networking.