If the mentioned error appears when you try installing the application on your computer, open the package file with any explorer. After you did this, right click on the PKG file and select the Show package content, open the Resources folder, and in that folder, find and decompress the file that has the .PAX.GZ extension (i.e. PhotoStudio.pax.gz). After you did this, copy the application file to the Application folder and open it. You should be able to overcome the error message.
