Insufficient Software Channel Entitlements

Recently I've upgraded our Server from RHEL 5 to 6.5.
So after I finished the installation I tried to register this system into my account so I'm able to receive updates from YUM.
But when I try to register this server I receive the following message:

===========================================================================================
Error communicating with server. The message was:

Error Message:
Insufficient Software Channel Entitlements:

cfid8960  Red Hat Enterprise Linux Server (v. 6)

note: One of the above Software Channel Entitlement(s) are required
to provides access to: cid10486 Red Hat Enterprise Linux Server (v. 6 for 64-bit x86_64)
Error Class Code: 70
Error Class Info:
All available subscriptions for the requested channel have been exhausted.
Please contact a Red Hat Network Sales associate.
Explanation:
An error has occurred while processing your request. If this problem
persists please enter a bug report at bugzilla.redhat.com.
If you choose to submit the bug report, please be sure to include
details of what you were trying to do when this error occurred and
details on how to reproduce this problem.

===========================================================================================

It doesn't matter if I try it with:
- rhn_register
- subscription_manager register
- rhnreg_ks

And even the --force option doesn't work.
I've logged in as well, but I cant find the 'old' installation of this server on my account.
What do I need to do to re-register and get my updates :-).

Thanks in advance.