After 10.5.3 update, MacBook won't shut down.

After updating my new MacBook to 10.5.3, now the computer won't shutdown.
When I choose shutdown, the little cog appears and it will just stay there until I press and hold the power button.
I have run the disk utility and checked permissions.
Any suggestions?

Hold the power button for a few seconds until it shuts down. Should sort itself out when you turn it back on.

Thanks for the reply...
I already tried that. Shutdown is intermittent. This only started after I updated to OSX 10.5.3