Mirror isn't listed in Bugzilla as a component, thus my posting it here. The version of mirror shipped has a bug which prevents it from working with the new WU-FTPD. A patch to the ftp.pl is available from the mirror page on Sunsite. It also looks like you're shipping an older version than what's available on Sunsite, so updating the package to the latest version may be the simplest thing to do (and make sure the patch is included, of course)
*** This bug has been marked as a duplicate of 6831 ***