let me write the relations and durations of these actvities only as the rest of activities are irrelevant.
Activity B : (Dur: 2 days) (Pred: irrelevant) (Succ: G(SS), D)
Activity D : (Dur: irrelevant) (Pred: B, G) (Succ: Irrelevant)
Activity G : (Dur: 3 days) (Pred: B(ss)) (Succ: D)

and all are critical in the schedule

So as you can see, B is making G critical by affecting its start date, and Both B and G are pushing D with FS. since D is 1 day longer than B, there is a 1 day float for finishing B. So although Start of B can not move, and the program says Total Float is 0 and I understand that, still we could make B 1 day longer, and the job would not delay. but all types of floats still show 0. so does it mean, all types of floats only depend on start dates?