You appear to be confusing Win32::Registry usage with Win32::TieRegistry. Win32::TieRegistry doesn't define a HKEY_LOCAL_MACHINE variable.

Because this type of stuff is easy to confuse, I strongly encourage making it explicit what you are importing from each module:

use strict 'vars';
use warnings 'all';
my $Registry;
use Win32::TieRegistry( TiedRef => \$Registry );
my $CurrVer= $Registry->{"HKEY_LOCAL_MACHINE\\"
  . "Software\\Microsoft\\Windows NT\\CurrentVersion\\" )
  or  die "Can't open SW/MS/WinNT/CurrentVersion: $^E\n";
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        - tye (but my friends call me "Tye")