Add-SPShellAdmin: You need to have Machine administrator priviliges to run this cmdlet
While trying to add a new user to grant PowerShell script execution policies, I got this error message:
Add-SPShellAdmin: You need to have Machine administrator priviliges to run this cmdlet
Solution:
Although you are in the local server Administrator group, You must run the SharePoint Management Shell as Administrator. Simply right-click on SharePoint 2010/2013 Management Shell >> Choose “Run as an administrator”!
Alternatively, you can disable the UAC to avoid these kinds of issues. You may face this issue when you try to run cmdlets such as: Add-SPShellAdmin, Backup-SPFarm, New-SPWebApplication, Set-SPManagedAccount, etc.
Related article: How to disable UAC in Windows 2012?
Cannot add Administrator to the SharePoint_Shell_Access role of the database SharePoint_Config. A possible cause
of this error is that the account name was already added to the database as a login using a different user name than
the account name