When I updated Defender in Windows 8 Consumer Preview, the error code 80070666 appears. I've tried using the FixIt tool, but that is not compatible with the new operating system.

Is there a method to fix it? Thank you.

This error code is generally due to a Windows System damage or corruption. You might be better off reinstalling Win 8 CP to correct this error. To do so it might be a good idea to download the iso file again directly from MS (http://windows.microsoft.com/en-US/windows-8/iso) burn the iso file to DVD and do a Custom (Clean) install. This will give you a pristine installation and should fix this problem. System file corruption can be serious and lead to unbootable systems.