The application form you are trying to view is already open in another page.

If you do not wish to lose your data you should locate and open that page. 

If you are certain that you do not have your application open in another page, because you closed the page using the red x or the exit option in the file menu, then click on the reset link below.  This will reopen the form with the data that had been entered before you last clicked on the 'Next' button.