SRL Archive - Help

I have installed Java 8 but I'm not sure that Java creates a problem in my code.

Here is a piece of code that I think that creates a problem.

program new;

var
 i,stringa : integer;
 b,t : string;
begin
 i := 1;


 WHILE i <=19999 DO
    begin

 ClickMouse ( 390, 329, mouse_left );   //
 ClickMouse ( 390, 329, mouse_left );   //  This code taken string
 ClickMouse ( 390, 329, mouse_left );   //  in CHAT on Firefox.
 ClickMouse ( 390, 329, mouse_right );  //  Sets the ClipBoard
     wait (391);                        //  with the option Copy
 MoveMouse ( 458, 344);                 //  (right_click,
 ClickMouse ( 458,344, mouse_left );    //  then left_click Copy)

         duzinastringa := Length(getClipBoard());
         b := getClipBoard();

         if stringa <= 3 then duzinastringa := 4;
         
         t :=   b[duzinastringa-2];
      i := i + 1;
   end;

end.

Error: Access violation at line

t :=   b[stringa-2];

Most common ERROR is displayed when the stringa = 0.
That's why I put a line:

if duzinastringa <= 3 then duzinastringa := 4;

but error(Access violation) is still sometimes displayed. Please help