With OS X 10.10.3, Apple replaced both Aperture & iPhoto with a brand new product called "Photos". One of the changes that Apple made was how "Photos" integrates with 3rd party applications.
The most common way that people use their photos stored in "Photos" with 3rd party applications, is to simply drag the photos out and into the other application. "Photos" breaks that functionality, which unfortunately is how "Fun Photo Cube" was designed. There is a solution.