You might see the above error with: appcmd start site or appcmd stop site.
You need to Run as Administrator.
Running as a non-admin, you'll get the error:
c:\Windows\System32\inetsrv>appcmd.exe start site "Default Web Site" ERROR ( message:The W3SVC service is not available - try starting the service first. )
Running as an Admin, the command succeeds:
c:\Windows\System32\inetsrv>appcmd.exe start site "Default Web Site" "Default Web Site" successfully started.