After updating to Snow Leopard 10.6.8 (from leopard 10.5) and the restoration of configurations and saved files, I can't no longer turn off my iMac normally.
The shutdown option is restarting the iMac.
- Click on the Disk Utility located in Applications > Utilities > SOS tab.
- Select your primary drive and click "repair permissions".
- You can also make use of a small utility to fix this issue.
- Download and install Onyx: http://www.titanium.free.fr/download.php
- Launch program and allow it to scan the SMART status of hard disk and volume structure.
- Enter password when prompted
- Then click the "Automation"
- Check all boxes except "Display the contents of folders"
- Click "Run"
- Restart the Mac.
Thanks to pierrephoto
for this tip.