Well, I was able to find those keys with the second script, but the delete part needs some work to catch them. Good thing that isn't the issue I'm trying to solve. ;-)

Here's the fixed version:

use Win32::TieRegistry(Delimiter=>'/');
$| = 1;

sub process_hidden
{
  my ($root, $tgt) = @_;
  print "HIDDEN REGISTRY KEY FOUND:\n$root/$tgt\n\n";
  print "Delete or Keep? [D/k]  ";
  $_=<>;
  chomp;
  if ( ! /k/i )
  {
    delete $Registry->{$root}->{$tgt};
  }
}

sub check_content
{
   for ( keys %{$Registry->{$root}} )
   {
      &check_content("$root/$_")   if exists $Registry->{"$root/$_/"};
      &process_hidden($root,$_)  if (length($_) > 256
                                 ||  index($_,"\0") >= 0);
   }
}


&check_content("CUser/TEST/");
[download]

Also, my regedit had no problem deleting that key ... perhaps that is an old bug? The page you reference is from 1999 ...