I've just realized that my version of Isadora 2 is attempting to open the file instead of Isadora 3
You can right-click these menu icons, and select 'open file location'. In the folder that opens will be these 2 Isadora shortcuts.. If you check properties on them you can determine which is for Isadora 3 and for Isadora 2.. then rename them accordingly. These Icons will then show-up in your menu with the name you gave them..
I do this with every beta version I install, so that I can have dozens of Isadora versions installed.