yum出现如下问题

SturdyEagle

Repository updates-released already added, not adding again
Repository base already added, not adding again
Setting up Update Process
Setting up repositories
base                                                            1.1 kB 00:00
ftp://ftp.tsinghua.edu.cn/mirror ... epodata/repomd.xml: [Errno 4] IOError: [Errno ftp error] 550 Can't change directory to repodata: No such file or directory
Trying other mirror.
Cannot open/read repomd.xml file for repository: updates-released
failure: repodata/repomd.xml from updates-released: [Errno 256] No more mirrors to try.

我用gftp登录上去看了,明明这两个目录都在,erpodata/repomd.xml也有,这是怎么回事呢?
我第一次用yum,教育网的.
下面是我的yum.conf文件:
[main]
cachedir=/var/cache/yum
debuglevel=2
logfile=/var/log/yum.log
pkgpolicy=newest
distroverpkg=redhat-release
tolerant=1
exactarch=1
retries=3
obsoletes=1
gpgcheck=1

# PUT YOUR REPOS HERE OR IN separate files named file.repo
# in /etc/yum.repos.d

[base]

name=Fedora Core 4

baseurl=ftp://ftp.tsinghua.edu.cn/mirror/download.fedora.redhat.com/pub/fedora/linux/core/4/i386/os

[updates-released]

name=Fedora Core Updates

baseurl=ftp://ftp.tsinghua.edu.cn/mirror/download.fedora.redhat.com/pub/fedora/linux/core/updates/4