Yep. There was a recent update to yum-rhn-plugin that introduced a bug that causes this exact problem (version 0.5.4-22.el5_7.1). The long-term solution is to get the version of yum-rhn-plugin that was put out this week (version 0.5.4-22.el5_7.2).
I just set up a remote command on my machines that installed yum-rhn-plugin specifically.
Short-term, you can do:
-yum clean all
-rm -rf /var/cache/yum/*
Funny note about the bug: it is only triggered by running 'rhn_check' with no options. Adding any number of '-v' after the command doesn't trigger it.
my updates are failing when i try to update my satellite clients using my redhat satellite server running rhel 5.7. I schedule the event and after it gets picked up, it fails with the error
Client execution returned "Error while executing packages action: empty transaction []" (code -1)
i am able to run the yum update on the client and it will perform the updates but when going through the satellite server it errors out.