It is extremely important that the files in the ZData folder not be modified. Doing so can lead to crashes and other problems, not to mention the possibility of causing difficulties with future ZBrush upgrades. The exception to this is the ZPlugs folder (where you can place ZScripts that will be run when ZBrush launches). If you have already modified your ZData folder, it should be restored to its original content. If you don’t have a backup, you can do this by executing the uninstaller and then reinstalling ZBrush. It will not be necessary to re-register Z2.