Thks for your cooperation....I answer myself
The problem was that I got a negative value to get a char into string,substring.
My problem is in PHP the negative value is not a problem so i didnt see the value was negative. There is no limitattion with string , I supopse this because with string smaller it worked so fine but now i solve the problem.
So sorry but I am so newbie and really cost to me to B4A. I used to use this for windows and it was so eassy....this is a little more complicated....:sign0027: