Neutered dog trying to get up on female?

We have two dogs a male who is now 2.5 yrs and he is neutered since 1! Our female is two and she is in heat. This is her 3rd wk on heat. Just this week our male dog has been trying to get up on her, he's not very successful it's like he doesn't know what to do!! But every evening for about an hour or so this ritual goes on where they are barking and yapping at each other coz she's trying to get up on her. Why is my male neutered dog doing this? We thought getting him done would stop it ?