POP3 server not working properly

I have the POP3 service running on my Windows Server 2003 machine. For some
reason, it isn't easy to connect to it. I've restarted both the service and
the machine, and rebooted the clients I'm using as well, but I consistently
get this error:

Your server has unexpectedly terminated the connection. Possible causes for
this include server problems, network problems, or a long period of
inactivity. Account: 'xxx.xxx.net', Server: 'xxx.xxx.net', Protocol: POP3,
Port: 110, Secure(SSL): No, Error Number: 0x800CCC0F

I have tried everything I can think of to resolve this, but it just won't
work. This is an Outlook Express client on Windows XPro.

I also have Outlook 2003 on another XP Pro machine and while it doesn't
always work, it is working at the moment.

While I was getting this error on both clients, I was able to telnet in on
port 110 and connect. I couldn't get the email from the server, though, even
using a client ON the server.

Ideas? Suggestions?

Thanks,

David