sub BrowseForFolder {
   undef $Win32::FileOp::Error;
   my ($hwndOwner, $pidlRoot, $pszDisplayName,
       $lpszTitle, $nFolder, $ulFlags,
       $lpfn, $lParam, $iImage, $pszPath)
      =
      (GetWindowHandle(), "\0"x260, "\0"x260,
       shift() || "\0", shift() || 0, (shift() || 0) | 0x0000,
       0, 0, 0, "\0"x260);

   $nFolder = CSIDL_DRIVES() unless defined $nFolder;
....

##</code><code>##

sub BrowseForFolder {
   undef $Win32::FileOp::Error;
   my ($pidlRoot, $pszDisplayName, # removed first var
       $lpszTitle, $nFolder, $ulFlags,
       $lpfn, $lParam, $iImage, $pszPath, $hwndOwner) # and put it last
      =
      ("\0"x260, "\0"x260,
       shift() || "\0", shift() || 0, (shift() || 0) | 0x0000,
       0, 0, 0, "\0"x260, shift());

   $hwndOwner = GetWindowHandle() unless defined $hwndOwner; #added for if $hwndOwner is undef

   $nFolder = CSIDL_DRIVES() unless defined $nFolder;

##</code><code>##

my $windowid = hex ($main_window -> id);
my $dir = BrowseForFolder("Relative to \$main_window", undef, undef, $windowid);

##</code><code>##

title => ... 
filters => ...
defaultfilter => ...
dir => ...
handle => ...
options => ...
etc...
##</code><code>##

my $windowid = hex ($mw -> id);

my $directory = BrowseForFolder (
	-title => "Choose Directory:",
	-CSIDL_opt => 'CSIDL_DRIVES,
	-BIF_opts => 'BIF_RETURNFSANCESTORS',
	-open_folder => 'C:\Perl\site\lib\Win32',
	-handle => $windowid,
	);