On page 397-398 immunities are mentioned. Now the question is how to handle normal weapons immunities.
The first paragraph of the power mentions it working as hardened armor:
Effectively, the critter has a Hardened Armor rating equal to twice its Essence against that particular kind of damage (see Hardened Armor, p. 397).
Then though the 2nd paragraph mentions immunity to normal weapons and immunity to age and the following excerpt:
Some Immunities function slightly differently, because the attack they protect against doesn’t do damage, per se
Now the question though is what is it about weapons?
For age it is clear that there is no damage at all, and no effect at all. But weapons is the question. Especially as as far as I remember they are one of the only "Immunities" that critters have that comes into effect where damage is directly involved. Aside from acid, fire,... weapons are one of the few things that could do damage to a critter and where imunities come into effect.
So the question is: How is that rules part now really meant?
If that works as complete immunity for weapons I have to say that is one of the most drastic changes to SR4.......as there you had normal weapons vs. hardened armor AND even mind fighting rules that allowed non mages to fight spirits.