Giant Ambush Beetle not attacking magic rulings

[Sphinx]

if I play a Giant Ambush Beetle and I target some creature and I attack with another creature (but not with Giant Ambush Beetle) is the targeted creature allowed to block at all (since it was supposed to block the Giant Ambush Beetle which is not attacking)?

[Arix]

Yes, it can block. It doesn't matter that it was supposed to block the Beetle. It isn't blocking the Beetle and is therefor efree to block your other creature.