The remote host is missing an update to wzdftpd announced via advisory DSA 1452-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%201452-1

k1tk4t discovered that wzdftpd, a portable, modular, small and efficient ftp server, did not correctly handle the receipt of long usernames. This could allow remote users to cause the daemon to exit. For the stable distribution (etch), this problem has been fixed in version 0.8.1-2etch1. For the old stable distribution (sarge), this problem has been fixed in version 0.5.2-1.1sarge3. For the unstable distribution (sid), this problem has been fixed in version 0.8.2-2.1. We recommend that you upgrade your wzdftpd package.