ProFTPd goes crazy every few days

[Self-Defence]

Hi,

I've got a Fedora 5 server set up witch has now got an uptime of over 80 days. But every few days some times one sometimes three or four days the ProFTPd daemon gets messed up.
If I try to connect to it and type in the user & pass just says that it can't authentuicate and gives a 501 (I think) error and a strange charater(rectangular shape with four ones or zeros inside). And that's it no user can logon and nothing is accepted until I restart the daemon.

I've been searching for the cause but there's nothing in the system logs or maybe I just don't know where to look.

Anyone have any bright ideas what to do?

[Self-Defence]

Anyone have any ideas?

[Self-Defence]

Well the ProFTPd finaly froze again.
This is the error I keep getting if it freezes:
220 FTP Server ready.
USER ********
500
not understood

Anyone have any ideas what this error means?

[Self-Defence]

Aparently this character
means HEADING, START OF, START OF HEADING but I still don't know why it starts doing this.