Can free action focus power rolls be made in the same turn as full and half action attacks?
I think they can, for the following reasons.
Page 188 of the core book says that you cannot take hte same half action twice.
Page 9 of the errata says: "Making a focus power action is the psychic equivalent of a standard attack action, and counts as such for the purposes of determining what else a psyker can do in a round. Therefore a psyker who uses a half action power cannot make another half action standard attack on the same round. A psyker may manifest only one ability per round with the exception of the resist posession power. A psyker is required to roll at least one die to manifest an ability."
The use of "therefore" implies (to me, at least) that the reason that you can't make a half action focus power and half action attack the same turn is because of the stipulation on page 188 of the core book that you can't make the same half action twice (and because half action attacks are "equivalent" to half action psychic powers). To me, this would still allow you to make free action focus power rolls the same turn as you make full action and half action attacks. Even though those free action focus power rolls are standard attack actions (as stated in page 9 of the errata), they can be taken the same turn as full action and half action attacks, since the stipulation against taking two of the same type of action in the same turn is limited to half actions.
There are also gameplay reasons I think free action focus power rolls are intended to be taken the same turn as fulll and half action attacks:
Firstly: Let's say I have WS 60 (As my psyker does), and want to kill an enemy (obviously). If i cast precognitive strike this turn, I have a 33% increased chance of hitting him (since with Precognitive strike I hit on anything below 80, and without it, I hit below 60.) This means that I increase average damage output by 33% (Yes, this is an abstraction/generalization, but there is no practical way for me to include every possible detail/weapon combo/situation, I'm just assuming that it will increase damage I deal (on average) by 33%.) However, with that damage increase comes a decrease, since I will only be hitting every other turn. So, my damage will increase by 50% as a result of that. This leaves me doing less damage than I would have if I didn't use precognitive strike. Of course, it lets me do something like run or hide or take a defensive stance on the turn i cast it, but those things aren't really valuable to me since I can already dodge/parry 3 times total and only have to roll under 70/80 to do that. So I odn't usually want to play defensively like that,/I usually go right into combat. and want to be able to attack the whole time. So, as far as I can tell, precognitive strike only benefits people whose weapon skill is horrible (if it means that you can't attack the round you cast it).
Secondly, Pyschic soldier (from Ascension) allows you to make focus power rolls for less "time" (half action becomes free action, full action becomes half action). This seems to me to indicate that you're supposed to use it to cast psychic powers on a turn that you are fighting.
Sorry this is so lengthy... I hope someone can explain where either me or my GM has gone wrong with this rule. (He says you can't make free action focus power rolls the same turn as any attacks, with the exception of the force weapon psychic power and resist possession.) I also hope this hasn't been answered already...I searched for it and couldn't find anything, but might have used the wrong search terms :/