Oracle Linux yum is not working after update

I've updated my Oracle Linux 6.4 server to Oracle Linux 6.8 which is registered to spacewalk server. But after update, yum commands are not working in server. [root@j4server tmp]# yum update Loaded plugins: aliases, changelog, kabi, presto, refresh-packagekit, rhnplugin, security, tmprepo, verify, : versionlock Traceback (most recent call last): File "/usr/bin/yum", line 29, in yummain.user_main(sys.argv[1:], exit_code=True) File "/usr/share/yum-cli/yummain.py", line 298, in user_main errcode = main(args) File "/usr/share/yum-cli/yummain.py", line 115, in main base.getOptionsConfig(args) File "/usr/share/yum-cli/cli.py", line 229, in getOptionsConfig self.conf File "/usr/lib/python2.6/site-packages/yum/__init__.py", line 911, in conf = property(fget=lambda self: self._getConfig(), File "/usr/lib/python2.6/site-packages/yum/__init__.py", line 363, in _getConfig self.plugins.run('init') File "/usr/lib/python2.6/site-packages/yum/plugins.py", line 184, in run func(conduitcls(self, self.base, conf, **kwargs)) File "/usr/share/yum-plugins/rhnplugin.py", line 115, in init_hook login_info = up2dateAuth.getLoginInfo() File "/usr/share/rhn/up2date_client/up2dateAuth.py", line 219, in getLoginInfo login() File "/usr/share/rhn/up2date_client/up2dateAuth.py", line 167, in login if readCachedLogin(): File "/usr/share/rhn/up2date_client/up2dateAuth.py", line 133, in readCachedLogin expireTime = float(li['X-RHN-Auth-Expiration']) KeyError: 'X-RHN-Auth-Expiration' It is throwing this output. When I try to disable rhn-plugin, yum commands works, list packages on spacewalk but as you guess can't install them. Do you have any ideas about this situation? Thanks for any help!