1. Download the info.plist file attached to this reply (use a web browser like Google Chrome or FIrefox if you encounter any difficulty downloading this file).
Right click your Starry Night High School program and select "Show package Contents". Open the Contents folder and replace the info.plist you see with the one I attached.
To right click on Mac, hold down the control key, and then click either your touch pad or mouse.
2. Download this update for SNHS 6.4.3:
Run the updater. This will revert your SNHS to 6.4.3. This should make SNHS compatible with OSX 10.5.8.
Don't update to 6.4.6 afterwards. Just stay at 6.4.3.
You will not be able to run the updater until the info.plist has been replaced.