The software described in this documentation is either no longer supported or is in extended support.
Oracle recommends that you upgrade to a current supported release.

1.4.9 Clients Might Have to Re-register After an Upgrade

After a Spacewalk server is upgraded, Spacewalk clients might have to re-register with the Spacewalk server. The web interface shows the clients as registered, but when you run the rhncfg-client command on the client, errors such as Authentication failed: Invalid digital server certificate are displayed.

If this happens, use either the rhn_register or the rhnreg_ks --force command to re-register the client.