OK. Modified version.
Log( 1, 10, "Renaming files to %%parent_folder_name%%[_N].*" );
@var $src_path = GetSourcePath();
@var $arr = PathGetParts( $src_path );
@var $name = $arr[0];
@var $prefix = StrReplace( PathGetPathPart( $src_path, 1 ), $name, "" );
@var $n = StrRFind( $prefix, "\\" );
if ( $n > 0 )
{
  $prefix = StrSub( $prefix, $n + 1, StrLen( $prefix ) - $n - 1 );
  @var $i;
  @var $c;
  @var $s;
  @var $file;
  @var $old_file;
  @var $files;
  @var $mask = "*";
  $arr = GetSourceSelectedPaths();
  for ( $i = 0; $i < arrayCount( $arr ); $i++ )
  {
    $file = $arr[$i];
    if ( IsFolder( $file ) )
    {
      continue;
    }
    $s = PathGetNamePart( $file, 1 );
    $n = StrRegExpFind( $s, "\d+$" );
    if ( $n < 0 )
    {
      $s = "";
    }
    else
    {
      $s = StrSub( $s, $n, StrLen( $s ) - $n );
    }
    $name = $prefix + $s + $mask;
    $s = PathGetFileExtPart( $file );
    $name = $name + $s;
    $files = FindFiles( $src_path + $name );
    $n = arrayCount( $files );
    $s = StrReplace( $name, $mask, "" );
    $n = 0;
    $c = 0;
    while( $n < arrayCount( $files ) )
    {
      while( $n < arrayCount( $files ) )
      {
        $old_file = $files[$n];
	 $old_file = PathGetNamePart( $old_file );
	 
        if ( StrIsEqual( $s, $old_file ) )
        {
          $c++;
          $s = StrReplace( $name, $mask, "_" + numtostr( $c ) );
          $n = 0;
          break;
        }
        $n++;
      }
    }
    RenameFile( $file, $s, "RENAME_RO" );
  }
}
else
{
  Log( 1, 10, "It seems parent folder is root. Renaming impossible." );
}