"Load Hive" option grayed out

Question

I want to load the HKEY_LOCAL_MACHINE hive from another installation of Windows (e.g. X:\Windows\System32\config\SYSTEM), but apparently I can't load the hive because the "File -> Load Hive" menu item is disabled:

Answer 1

You need to load a hive into a specific key, so it's necessary to select a key first:

You can load hives into HKEY_LOCAL_MACHINE or into HKEY_USERS.

Once you've clicked one of these, the "Load Hive" menu item will immediately become available:

Answer 2

Even if you chose the correct key to load a hive into, this may result from insufficient user rights. If you're running under a user account and open regedit without admin rights, you may not be able to load a hive.
I have seen that on my own business laptop, in which I have a user account without local admin rights.