I'm not looking for help. This is just a FYI for POTN members who uses Aperture.
My nephew got an update message on his AppStore. But when he tried to update Aperture it crashes on him. He's getting The application could not be downloaded error. "PKInstallSandbox-tmp" couldn't be removed because you don't have permission to access it.
He ended up using TimeMachine to restore to the previous working version.
As far as I can guess. It's either a problem with Aperture or a problem with the AppStore. But for now I'll skip the update until more info becomes available.

