A chapter on Group Policy troubleshooting? Am I implying that things can go wrong during the processing of Group Policy Objects? Am I insinuating that Group Policy administrators may not be perfectly planning out every single setting that they put inside every single GPO? How insulting to both Microsoft and to you admins!
Alas, nothing and nobody is perfect. Even in the smallest of environments, if you use Group Policy to deploy settings, you will eventually need to troubleshoot some aspect of this process. Most of the time, Group Policy issues are caused by human error. It is very easy to deploy settings to the wrong workstations or users, or forget to set filtering, or link something before you have fully tested it. It is also easy to create conflicting settings packages, or to deny permissions and forget about them, only to cause you grief down...