Window not appear when using Webutil | Oracle Forms 12c

Hello,

I've created one form that using webutil functionality for saving text file as follow and it is working fine.

:CTRL_BLK.TXT_DIR_PATH :=

  WebUtil_File.File_Save_Dialog (

     directory_name   => null,

     File_Filter      => '|text file|*.txt|',

     Title            => 'Select Directory where you want save your Text File.');

MYFILE := CLIENT_TEXT_IO.FOPEN (:TXT_DIR_PATH, 'W');

      CLIENT_TEXT_IO.PUT_LINE (MYFILE, V_text);

      CLIENT_TEXT_IO.FCLOSE (MYFILE);

But some times when running this form window will not appear and it will show blank page (Menu and toolbar only will appear without the form content)