The error message "Starry Night can’t be opened because it is from an unidentified developer" results from new security measures in Mountain Lion 10.8.x.
- Right-click (or control-click) the Starry Night application and choose “Open”
- Click the “Open” button at the next dialog warning to launch the app anyway
Please see the following KB article for further discussion:
I am able to open "Starry Night" on my MacBook Pro, but can't open it on my iMac. Same Mac OS 10.8.3
Please submit a ticket regarding the iMac. I'm sure we can resolve the issue.