I had the same problem, but a slightly different solution was called for. The problem in this case was the class of the File Owner, rather than the class of the View. To set this, I had to click the "backwards play" icon in the lower left corner of the Interface Builder window, and options then appeared that isolated the characteristics of the File Owner, the First Responder, and the View. Clicking on the first one (a large transparent box), enabled me to then set its custom class as suggested above.