I have been working quite allot with Group Policy objects and have recently been involved in troubleshooting them. As a last resort if all else fails, and your Default Domain Policy and Default Domain Controller Policy is beyond repair,or somehow has been deleted. Then you can use a utility which is shipped out with Windows 2003 which is DCGPOFIX.EXE. This utility comes with several prerequisites
Please note however this will restore the Default Group Policies to how they were just after the Active Directory was installed.
By using the following switch
However please take note of the following kbarticle when using this Utility http://support.Microsoft.com/kb/833783/en-us. This highlights that the DCGPOFIX.EXE utility may not be able to return the security settings to precisely the original state. Therefore further remedial work may have to be undertaken. It is therefore recommended that you should use the GMPC to make regular backups of your Policies, to avoid having to use this utility.