Description of problem:
When registering a system through an activation key (sub-mgr --activationkey=foo) that has a problem in it (eg. Pool with id ff80808 could not be found) leaves the system itself thinking it is not registered. Katello, however, lists the system as registered (though w/o any subscriptions, even the valid ones, in the activation key).
Further attempts to register the system will result in "Validation failed: Name has already been taken" errors from sub-mgr.
Just a quick note - for activation keys there is a transaction implemented for subscriptions. If anything fails Katello tries to unsubscribe already subscribed entitlements. But activation is out of this transaction, so it does not get rolled out.
*** This bug has been marked as a duplicate of bug 803814 ***