dunno that module, but when passing the arguments what about:

sub OpenFile_Click {
    $FileName= Win32::FileOp::OpenDialog(

        'title' => 'Open Text File',
        'defaultfilter' => '1'
    );
    # print ("Want me to open $Filename ?\n");
      exit(0);
   }
[download]

Well at least this is how CGI.pm likes parameters to get passed :-)

Have a nice day
All decision is left to your taste