fedora 17 yum error

edit

When I try to do 'yum update' or 'yum install', I get this error:

        self._metalink = metalink.MetaLinkRepoMD(result)
      File "/usr/lib/python2.7/site-packages/yum/metalink.py", line 186, in __init__
        root = xmlparse(filename)
      File "/usr/lib/python2.7/site-packages/yum/misc.py", line 1195, in cElementTree_xmlparse
        return __cached_cElementTree.parse(filename)
      File "<string>", line 62, in parse
      File "<string>", line 37, in parse
    RuntimeError: cannot load dispatch table from pyexpat

I printed the file for which xml parsing is failing. It is /var/cache/yum/i386/17/fedora/metalink.xml.tmp So, I did:

yum clean headers  
yum clean metadata  
yum clean packages

But to no avail. I still get the error.

Any ideas?