When attempting to register the Active Directory Schema Snap-in (also known as the Schema Console or Schema MMC console) using Windows Vista, Windows 7, Windows Server 2008, or Windows Server 2008 R2, you may need to run the command from an elevated command prompt. Otherwise, you could see the following error after running the registration command regsvr32 schmmgmt.dll
This is because User Account Control (UAC) might be limiting your capabilities even if you logged on using an account that is a member of the Schema Admins group. You do need to login or start an elevated command prompt using an account that is a member of the Schema Admins group.
To open an elevated command prompt, click the Start button in the toolbar, type Command Prompt. Then, right-click Command Prompt from the Start menu and click Run as administrator.
When the Schema Management dll is registered (schmmgmt.dll) you will see a successfully registered message.
There are many articles in the TechNet library discussing how to install the Schema Snap-In. Some apply to earlier operating system versions where running from an elevated command prompt was not necessary.