When updating the ADMX Central Store from Windows 10 to Windows 10 v1511, you may encounter the following error when attempting to view or edit group policies:

Administrative Templates

Namespace ‘Microsoft.Policies.WindowsStore’ is already defined as the target namespace for another file in the store.

File \\domain.fqdn\SysVol\domain.fqdn\Policies\PolicyDefinitions\WinStoreUI.admx, line 4, column 80

A similar problem is referenced in KB 3077013 but basically also applies to this issue:

1. On a domain controller, using Explorer, navigate to the ADMX Central Store:
   ...\SYSVOL\domain\Policies\PolicyDefinitions
2. Delete the file WinStoreUI.admx and all occurances of WinStoreUI.adml (under each language folder, such as en-US).

If you are not using anything from the WinStoreUI.admx template, you're done. If you have configured settings that use the template (Windows Store), you will have to perform the following steps as well in order not to break the group policy in which they are configured:

1. Rename WindowsStore.admx to WinStoreUI.admx.
2. In each of the language folders (such as en-US), rename WindowsStore.adml to WinStoreUI.adml.

Although you could ignore the problem, note that this will break the group policy Settings view in GPMC.