Description of problem:

yum appears to fail when loading plugin rhnplugin.

Version-Release number of selected component (if applicable):
yum-rhn-plugin-0.5.3-6.el5_2.6
yum-3.2.8-9.el5_2.1
python-2.4.3-21.el5

How reproducible:
all the time.

Steps to Reproduce:
1. install above software
2. yum check-update
3.
  
Actual results:
[root@mg ~]# yum check-update
Loading "rhnplugin" plugin
Traceback (most recent call last):
  File "/usr/bin/yum", line 29, in ?
    yummain.main(sys.argv[1:])
  File "/usr/share/yum-cli/yummain.py", line 85, in main
    base.getOptionsConfig(args)
  File "/usr/share/yum-cli/cli.py", line 163, in getOptionsConfig
    disabled_plugins=self.optparser._splitArg(opts.disableplugins))
  File "/usr/lib/python2.4/site-packages/yum/__init__.py", line 183, in _getConfig
    self.plugins.run('init')
  File "/usr/lib/python2.4/site-packages/yum/plugins.py", line 169, in run
    func(conduitcls(self, self.base, conf, **kwargs))
  File "/usr/lib/yum-plugins/rhnplugin.py", line 110, in init_hook
    login_info = up2dateAuth.getLoginInfo()
  File "/usr/share/rhn/up2date_client/up2dateAuth.py", line 211, in getLoginInfo
    login()
  File "/usr/share/rhn/up2date_client/up2dateAuth.py", line 159, in login
    if readCachedLogin():
  File "/usr/share/rhn/up2date_client/up2dateAuth.py", line 120, in readCachedLogin
    data = pickle.load(pcklAuth)
  File "/usr/lib64/python2.4/pickle.py", line 1390, in load
    return Unpickler(file).load()
  File "/usr/lib64/python2.4/pickle.py", line 872, in load
    dispatch[key](self)
  File "/usr/lib64/python2.4/pickle.py", line 894, in load_eof
    raise EOFError
EOFError

Expected results:

list of updates needed for said system.

Additional info:
yum -t check-update doesn't fail but also doesn't show list of packages that need to be updated :-)