How do I read from registry HKEY_LOCAL_MACHINE?

I'm having a hard time getting any reads from the registry with the root key HKEY_LOCAL_MACHINE.

var
  reg : TRegistry;
begin
  Reg := TRegistry.Create();
  Reg.RootKey := HKEY_LOCAL_MACHINE;
  if Reg.OpenKey('\SOFTWARE\Microsoft\Microsoft SQL Server',false) then
  begin
    Result := reg.ReadString('InstalledInstances');
    ....

I'm trying to get the values from the InstalledInstances Key:

At first I thought the code doesn't work. I then tried reading different keys under HKEY_LOCAL_MACHINE with the same results. Is there some kind of permissions thing I'm not getting?

If I use the same code for reading under HKEY_CURRENT_USER, that works fine and I get the key values. But under HKEY_LOCAL_MACHINE I can't open any key.

This also doesn't allow me to open:

Reg := TRegistry.Create(KEY_ALL_ACCESS);

When reading values from the HKEY_LOCAL_MACHINE root node, you need to use TRegistry.OpenKeyReadOnly() or change the TRegistry.Access property to either KEY_READ or KEY_EXECUTE. Otherwise, access to the Registry by your application will be blocked by UAC (User Account Control), as it is required to have elevated privileges in order to modify any key under the HKEY_LOCAL_MACHINE root node due to security settings.

Another way is to start your application with elevated privileges (Run As Administrator).

This is not required (although it is still desirable) when reading or modifying the Registry under the HEY_CURRENT_USER root node, since the current user already has the needed privileges in order to fully modify its own Registry keys.

EDIT: As for reading or writing REG_MULTI_SZ registry values I recommend you check Read and Write registry entry of type REG_MULTI_SZ using Delphi