Another common problem is that TieRegistry, by default, requests quite a bit of access to the keys that it opens. This is most commonly a problem when someone wants read-only access to a key. This problem should produce a different error reason than the one you reported, but perhaps not in this case for some reason.

So try specifying that you want less access to the key and see if that helps:

$remote_key = $Registry->Open(
  "$machine/$root_key", { Access => "KEY_READ" } )
  or die "Can't read $root_key: ", regLastError(), "\n";
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For more sophisticated control over the level of access, you'll need to import some symbols:

use Win32::TieRegistry qw( :KEY_ );
# ...
$remote_key = $Registry->Open(
  "$machine/$root_key", { Access => KEY_READ()|KEY_SET_VALUE() } )
  or die "Can't read $root_key: ", regLastError(), "\n";
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        - tye (but my friends call me "Tye")