There are two ways: Adwords platform upper right hand corner, you should have a notification about some ad groups not having KWs or ads in them. You can click that notification and it will take you to a management screen for that. Or you can use the Adwords Editor, by clicking on the campaign, then ad groups and sorting by the notification status column on the left hand side of the top main section of the Adwords Editor screen. You should see a bunch of red circles (indicating error).