You may experience some issues while using appcmd.exe if the IIS configuration is invalid.
In this case, look at the error details and double check the applicationHost.config file.
Possible locations:
%windir%\System32\inetsrv\Config\applicationHost.config%windir%\SysWOW64\inetsrv\Config\applicationHost.config%SystemRoot%\Sysnative\inetsrv\config\applicationHost.config