Perl and LVN_COLUMNCLICK; works fine under WinXP x86, but not under Win7 x64. Why?

I have this perl subroutine that works fine under WinXP x86, sorting a column for a 32 bit application among other things, but under Win7 x64 this subroutine doesn't work at all. The others work fine(tabs switching, pressing buttons, etc). Any idea why?

sub function      
{
my @searchresultswindow_handle = FindWindowLike( @_[ 0 ], undef, undef, $searchresultswindow_id );
 if( !@searchresultswindow_handle  )
  {
   die "Cannot find window handle for searchresultswindow control\n";
  }
 else
  {
   printf( "searchresultswindow handle is %x\n", $searchresultswindow_handle[ 0 ] );

            $keysList=@searchresultswindow_handle[0] ;

        my $action = pack( "l l",
        0, #ptaction.x
        0 #ptaction.y
        );

        my $action_ptr = unpack( 'L!', pack( 'P',$action));

        my $str_buf = pack( "L L L l l L L L L l",
        $keysList, #nmh.hdr.hwndFrom hwnd
        0, #nmh.hdr.idFrom

        4294967188, #LVN_COLUMNCLICK ,#开发者_如何学Gonmh.hdr.code Code
        -1, #item
  13, #sub item
        0, #uNewState
        0, #uOldState
        0, #uChanged
        $action_ptr, #action
        0 #lparam
        );

          $lvitem = AllocateVirtualBuffer( $keysList, 5000 );
        WriteToVirtualBuffer( $lvitem, $str_buf ); 


  my $value =PostMessage( $keysList, 0x004E, 0, $lvitem->{ 'ptr' });
FreeVirtualBuffer( $lvitem );
}
}

The structures are packed differently on 32 and 64 bit systems.

on 32-bit:

0:000> dt tagNMHDR
notepad!tagNMHDR
   +0x000 hwndFrom         : Ptr32 HWND__
   +0x004 idFrom           : Uint4B
   +0x008 code             : Uint4B

on 64-bit:

0:000> dt tagNMHDR
kernel32!tagNMHDR
   +0x000 hwndFrom         : Ptr64 HWND__
   +0x008 idFrom           : Uint8B
   +0x010 code             : Uint4B