source: https://mohdzmaili.wordpress.com/2017/02/15/failed-to-open-or-edit-gpo/comment-page-1/#comment-30
Group Policy Object cannot be opened or edited with the error: Failed to open Group Policy Object. You might not have the appropriate rights.
Details: The volume for a file has been externally altered so that the opened file is no longer valid.
Solution:
- Get GPO GUID: from Group Policy Management Console (GPMC) –> choose GPO –> from right pane go to Details tab –> go to Unique ID field.
- Open the path: C:\Windows\SYSVOL\sysvol\<Domain>\Policies\<GPO GUID>\User
- Delete “registry.pol” file.
Note: if you have migrated SYSVOL replication type from FRS to DFSR, open the path: C:\Windows\SYSVOL_DFSR\sysvol\<Domain>\Policies\<GPO GUID>\User