I don't think there will be an error. Since the client is prompting for username/password it did not send the request yet. Once you type in username/password the authentication is succesful, so no error.
Or, do you think the request fails x number of times and therefore the client reprompts for username/password because of the failure? That would be odd as once you type in username and password it passes first try.
I wonder if it is a roaming thing and not a radius thing. Maybe the client tries to roam several times and fails, thus prompting for username and password. Maybe the aruba side is more open to the roaming event and thus it is just a re-auth instead of a failure?
In that case I owuld have to look at the cisco controller logs.