in the following thread there is a link to a script which will fix this problem (the thread won't let me add this as a Reply):
The script does indeed work, but there is one piece missing from the instructions. You must log in as an account that has Administrator privileges before running the script. The script will ask you to enter your Administrator password in a Terminal window, but that will only work if you have already logged in as that Administrator, and not as just some normal user account without Administrator privileges. I.e. it does not work like the normal, OS X Authentication dialog where you get to enter BOTH the Administrator account name and password.
--Bob