Why can't I push an update for tomcat6 packages on RHEL 6?

Issue

• I have a system with out of date tomcat6 package and when I try to push an updated version of tomcat6 I get a message stating that no updates are available.

• rhn_check reports that there are no packages available for the scheduled errata:

  Client execution returned "No packages from that errata are available" (code 39)

• Subsequent executions of rhn_check report that the package is already updated, although it's not:

  Client execution returned "Requested packages already installed" (code 0)