You've experienced a crash. Seems there may be a permissions bug with 10.5.8
Run DiskUtility in Applications/Utilities, Select your disk and click in "Verify Permissions", and let me know if anything was reported. If it was, click on "Repair Permissions" then try the game after the repair completes.
If that doesn't work, we suggest the following:
0) Open \Applications\Utilities\Terminal.app
1) Type the following line in and hit enter:
chmod -R 755 \Applications\MonkeyIsland101.app
Assuming the file is in the Applications folder. If it's a different location, you can drag-and-drop the file onto the Terminal folder and it will paste the path in.
1a) If it yells at you for permissions, you'll need to use admin privileges and use this line. If this doesn't work, you need to be on an admin account and do this process.
sudo chmod -R 755 \Applications\MonkeyIsland101.app
2) Repeat this process for each MonkeyIsland episode. You can cheat and hit the UP button once, then edit the 101 to 102 and so on.
Good luck! Let me know how it goes and if that fixes it.