I was just installing PowerShell on one of my Windows Server 2003 servers, when I encountered the error “You do not have permission to update Windows Server 2003. Please contact your system administrator.” Odd, especially considering that I was installing as the Domain Administrator, and that user should have more than enough permissions. A little bit of digging led me to MSKB 888791 which shows the permissions that are required in Group Policy to install the update.