I dont see what you problem is, omg. The reason you can't use the money, is that when you sell shares, the person you sold them to doesn't pay you for them until after 3 days.
You can buy new shares in that time, because the new shares dont have to be paid for until after three days, by which time you will have the money from selling the first lot.
But you can't go and do anything else with the money, for the simple reason that you don't have it yet !
