The reason behind the error was that not connection was selected.
Ok, clear.
I thougt when I clicked on the brute force check button I will get a fully filled screen due to the fact that I opened this from a current FTP connection.
When it was empty I saw the select connection button, so I thought I could select a FTP connection so the page will be filled automaticly. 
It differs however from your explanation.
Regards,
Erik
                            
Uses Visualcron since 2006.