It's the same procedure for all Toshiba HD DVD players.
Inside the firmware there is a value that functions as "run if current firmware version is lower than". Your current firmware version is 4000 (after installing 4.0), and all you actually do is to set this "run if lower than" value to 4001 (hex 0f a1).
Btw, have you tried emptying the "Persistent Storage". I have seen others report it cured similar problems.