Unknown error occurred while adding user to farm admins

Error message when you add a user into a Farm Administrators group in SharePoint Foundation 2010 or in SharePoint Server 2010: "An unexpected error has occurred"

SYMPTOMS

You add a user into a Farm Administrators group in SharePoint Foundation 2010 or in SharePoint Server 2010. In this case, you receive the following error message:

An unexpected error has occurred.

This issue occurs when you are not a local administrator.

To work around this issue, you must be a member of both the following groups on the server that is hosting the SharePoint Central Administration Web site:

·         Farm administrators group

·         Local administrators group

Check ULS logs for the error from administrative tools ->Event Viewer ->Windows logs -> Application -> trace the error in SP Foundation -> “Local administrator privilege is required to update the Farm administrator’s Group”

Add the user to local admins and logoff then log on