Hi,
I'd be happy to help you out with your question. Sorry for the inconvenience caused.
If the groups are not members of the local admins, they may receive an access denied message when calling WAC. This could be because the user needs to have administrative privileges to perform certain actions in Windows Admin Center. To create an admin account, you can use the Command Prompt utility and run it as an administrator. However, if you are trying to add an Active Directory group as a local admin and getting an access denied error, you may want to check this thread on the Microsoft TechNet forum for possible solutions for which I added as resource below as "Trying to make a group local admin, but access denied."
Additionally, Microsoft's documentation on common troubleshooting steps for Windows Admin Center may provide further insights into resolving issues with WAC for which I added as resource below as "Windows Admin Center common troubleshooting steps".
One possible reason for this issue could be that the ServerManagementGateway/Windows Admin Center service is not running on the server. You can check if the service is running by opening Task Manager > Services. Another possibility is that the user needs to be a gateway administrator to perform certain actions, as mentioned in Microsoft's known issues documentation for which I added as resource below as "Windows Admin Center known issues".
For more Information please refer to following resources :-
- Windows Admin Center Access Denied - https://techcommunity.microsoft.com/t5/windows-admin-center/windows-admin-center-access-denied/td-p/2247117
- How to still make an admin account if it says access denied - https://answers.microsoft.com/en-us/windows/forum/all/how-to-still-make-an-admin-account-if-it-says/7768f6ac-e3cb-4ca1-9148-6abb89dc8c28
- Trying to make a group local admin, but access denied.- https://social.technet.microsoft.com/Forums/lync/7e26a30f-a155-4163-9fb7-5502741518a7/trying-to-make-a-group-local-admin-but-access-denied-which-right-to-set-correctly?forum=winserverpowershell
- Windows Admin Center common troubleshooting steps - https://learn.microsoft.com/windows-server/manage/windows-admin-center/support/troubleshooting
- Configuring user access control and permissions - https://learn.microsoft.com/windows-server/manage/windows-admin-center/configure/user-access-control
- Windows Admin Center common troubleshooting steps - https://learn.microsoft.com/windows-server/manage/windows-admin-center/support/troubleshooting
- Windows Admin Center known issues - https://learn.microsoft.com/windows-server/manage/windows-admin-center/support/known-issues
- Managing user access to Windows Admin Center - https://techcommunity.microsoft.com/t5/windows-admin-center/managing-user-access-to-windows-admin-center/td-p/3260955
- How to configure gateway access for windows admin center - https://learn.microsoft.com/answers/questions/618892/how-to-configure-gateway-access-for-windows-admin.html
- Windows Admin Center frequently asked questions - https://learn.microsoft.com/windows-server/manage/windows-admin-center/understand/faq
- Windows Admin center gateway access permissions - https://answers.microsoft.com/en-us/windows/forum/all/windows-admin-center-gateway-access-permissions/2911c777-cb82-4e67-823b-17940f6b6d66
- User access options with Windows Admin Center - https://learn.microsoft.com/windows-server/manage/windows-admin-center/plan/user-access-options
If you have any other questions or need assistance with anything, please don't hesitate to let me know. I'm here to help.
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