Seems like new Group policies templates/ADMX are generating new errors when you edit your GPO’s.

“Namespace ‘Microsoft.Polices.WindowsStore’ is already defined as the target namespace for another file in the store. File \\domain\sysvol\domain\Polices\PolicyDefinitions\WinStoreUI.admx, line 4, column 80″

This errors is generate because there are two or more template/ADMX files that are referring to Windows Store settings.

Do a search for file content in your PolicyDefinitions folder for “Microsoft.Policies.WindowsStore” in our case two files had the same references: WindowsStore.admx and WinStoreUI.admx.

So Microsoft renamed a template/ADMX file, again, that’s the root cause and to get rid of the problem follow these simple steps:

1. Move these two files to a backup folder
2. Download the latest ADMX templates again (Windows 10 ADMX templates are located here: http://www.microsoft.com/en-us/download/details.aspx?id=48257)
3. Do one of the following steps
   1. Copy only WindowsStore.admx and en-US\WindowsStore.adml
   2. Copy all ADMX and at least the English language folder containing ADML files, en-US. Overwrite all files
4. Close Group policy management console and try again

A similar error was generate a while ago, more information here:

https://deploywindows.com/2015/08/25/windowslocationprovider-error-while-upgrading-windows-10-admx/