Rule 303.4g deals with an aura that enters the battlefield without a legal choice for what to enchant:
303.4g If an Aura is entering the battlefield and there is no legal object or player for it to enchant, the Aura remains in its current zone, unless that zone is the stack. In that case, the Aura is put into its owner’s graveyard instead of entering the battlefield.
The first Benevolent Blessing prevents the creature from being a valid choice for the new one. It sounds at first like 303.4g should apply, but it says that the new aura would remain in its zone... but it wasn’t in any zone ever, it’s a newly created token. So does the token get created at all? I don’t know of a rule other than 303.4g that would stop it from being created.
The other option I can see is that it gets created, and goes to the battlefield not attached to anything. But then it goes away the next time state based actions are checked, as per 704.5m.
This different could matter if you had something that triggered when it enters the battlefield.
I’m using Benevolent Blessing as an example, as it’s the only thing I could think of that would make it possible to have an aura already on the battlefield, while not having a legal choice for another aura that’s a copy of that aura.