File::Find::Duplicate seems to look for files with identical contents. If you just care about identical names, you can use File::Find:

#!/usr/bin/perl -w

use strict;
use File::Find;

find(\&wanted,'.');

use vars qw(%dirseen);
sub wanted
{
  return unless -d $_;

  if ($dirseen{$_})
  {
    print "Duplicate directory name $_ in $File::Find::dir\n";
  }
  $dirseen{$_}++;
}
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