[rhn-users] system entitled but cannot subscribe to channel?

[Herta Van den Eynde]

We have 7 entitlements for management service and 1 for update service. 
  I just installed Red Hat Advanced Server 2.1 and registered it.  It 
automatically got the 7th management service entitlement, but the Base 
Channel shows up as "(none)".  When I try to change it, I get the 
message that "This assignment would exceed your allowed subscriptions."

I'm confused: what's the difference between subscription and 
entitlement?  What do I need to do to register this system properly?

Herta