When an application on a Mac OS X system states that, it usually means that GateKeeper Security on your mac is causing the error message to occur. This happens at times with Capture 2 Recording Software on Mac 10.8.5 systems, but seems to be occurring on El Capitan as well.
Below is instructions from Apple on how to disable GateKeeper and allow applications to install.
https://support.apple.com/en-us/HT202491
After you've allowed GateKeeper to install apps from "Mac App Store and identified developers," try and open Studio One 3 Prime again.