So, let's try this again..
It appears that some mirrors have changed their directory layouts after submitting the mirror as a CentOS mirror. Unfortunately the mirror checking scripts aren't smart enough to fix the errors automatically, so some amount of manual work is needed. Here is a list of such changes that I've noticed:
Limestone Networks (US, TX): OLD: rsync://centos.mirror.lstn.net/ NEW: rsync://centos.mirror.lstn.net/centos/ OLD: ftp://centos.mirror.lstn.net/ NEW: ftp://centos.mirror.lstn.net/centos/
Your.Org (US, IL): OLD: rsync://ftpmirror.your.org/pub/centos/ NEW: rsync://ftpmirror.your.org/centos/
Energy Sciences Network (US, CA): OLD: rsync://linux.mirrors.es.net/linux-pub/ NEW: rsync://linux.mirrors.es.net/centos/
Syringia Networks (US, ID): OLD: rsync://mirrors.syringanetworks.net/centos/ NEW: rsync://mirrors.syringanetworks.net/CentOS/ (note that the proper spelling for the sponsor name is most likely Syringa Networks)
Hostcentral (Australia): OLD: rsync://mirror.as24220.net/pub/centos/ NEW: rsync://mirror.as24220.net/centos/
CSC / Funet (Finland): OLD: rsync://rsync.nic.funet.fi/pub/mirrors/centos.org/ NEW: rsync://rsync.nic.funet.fi/ftp/pub/mirrors/centos.org/
NLUUG (Netherlands): OLD: rsync://ftp.nluug.nl/CentOS/ NEW: rsync://ftp.nluug.nl/centoslinux/
Neterra LTD (Bulgaria): OLD: rsync://mirrors.neterra.net//centos/ NEW: rsync://mirrors.neterra.net/centos/
Ukrnames LLC ICANN (Ukraine): OLD: rsync://mirror.ukrnames.com/mirrors/centos/ NEW: rsync://mirror.ukrnames.com/centos/
Cyber Internet Services (Pakistan): OLD: rsync://stingray.cyber.net.pk/pub/centos/ NEW: rsync://stingray.cyber.net.pk/centos/ OLD: ftp://stingray.cyber.net.pk/pub/centos/ NEW: ftp://stingray.cyber.net.pk/centos/
National Sun Yat-sen University (Taiwan): OLD: ftp://ftp.nsysu.edu.tw/CentOS/ NEW: ftp://ftp.nsysu.edu.tw/Unix-like/CentOS/
TaiChung City Education Network Center (Taiwan): OLD: ftp://ftp.tc.edu.tw/Linux/Centos/ NEW: ftp://ftp.tc.edu.tw/Linux/CentOS/ (note: sponsor URL should point to www.tc.edu.tw instead of www.tcc.edu.tw)
Universidade Federal do Espírito Santo (Brazil): OLD: rsync://centos.ufes.br/CentOS/ NEW: rsync://centos.ufes.br/centos/
Could these changes please be applied to the list of CentOS mirrors? Thanks :)