Sure, he's allowed to make mistakes.. every player does. When Nani gives the ball away it's usually one of two things. Either he is trying to be too clever and messes up- frustrating to watch but it's the price of trying something special, or he derps out and passes without any awareness of where the defenders are and gets easily cut out.
The latter is pathetic for a player with his amount of talent, its very understandable why some fans look at such basic errors and in a game where he didn't get any goals/ assists say he was bad. They are wrong, in my opinion. He was fairly productive and had a few great touches, but I agree he is a very frustrating player.