From the couple of time I have seen of this one it has been permissions being broken so before anything else give it the old mac universal fix:

Run Disk Utility:
Applications/Utilities/Disk Utility.app

Then select your Harddisk and hit repair permissions.

If you are unable to run Disk Utility this way you can boot off your install CD, put it in, reboot and hold down C on the keyboard till it boots. When the installer begins open Disk Utility from the menubar at the top of the screen.

Its not a guaranteed fix but its being giving good results for me