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, 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