Setting the RightPageIndex throws exceptions if the RadBook ItemContainerGenerator is not yet started

As a workaround you can set the property controlling the RightPageIndex in a dispatcher: 
this.Dispatcher.BeginInvoke(new Action(() => { dataContext.CurrentIndex = 2; }));

Another workaround would be setting the desired index after the containers have been generated. Use the ItemContainerGenerator.StatusChanged event and perform a check whether ItemContainerGenerator.Status is equal to the status "GontainersGenerated". If that condition is satisfied then setting the RightPageIndex should not throw exception.