What does it mean?

FTP site does not have unlimited access: physical connection or administrator allocation policy in a number of anonymous users of the site-specific. When this figure exceeds all who receive this message try to login.

What can you do about it?

As long as continue to work until you lucky. However, in a busy Web site (such as Netscape announced that the week after), or a very limited access rights, you may luck. If so, please check the web site has a mirror, and try one.