Cannot attach subscription to my registered RHEL 6.2

Hello,

I've successfully registered my RHEL 6.2 system (I have to use this rather old version), but can't attach it to my subscription.

When I Run Auto-Attach in the Customer Portal it tells me "Subscriptions have been auto-attached successfully", but nothing changes. In a terminal on the machine

simply returns "Status: Not Subscribed". Finally, when I try , I get "Too many content sets for certificate Red Hat Enterprise Linux Developer Suite. A newer client may be available to address this problem. See kbase ....". The Knowledge Base article suggest to upgrade my subscription-manager, but omits to say how. I failed to upgrade it via yum, but without a subscription I don't have any repos anyway.

As subscribing seems to be a substantial and common process, am I missing something obvious?