If you get such problem as this when using YUM on RHEL system :
# yum install xxxxx
Loaded plugins: product-id, refresh-packagekit, rhnplugin, security,
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
This system is receiving updates from RHN Classic or RHN Satellite.
Setting up Install Process
No package xxxxx available.
Error: Nothing to do
And your system is regularily on RHEL site, with a license, here is what can be done :
# subscription-manager unregister
# subscription-manager clean
# subscription-manager register