Hmmmm... well, if B cannot ally with A, then it doesn't really matter whether A could ally with B, does it? But this should be fixed definately as to avoid confusion. This mistake is probably due to us changing the objectives over and over, adding new warbands to the Silent Threat and at one point the Threat could no longer ally with the Protectorate, but I probably forgot to amend the Protectorate's entry. I will look after this for the next errata.
The main rulebook has not (yet!) been updated due to some technical difficulties. All the individual PDFs (if you browse through the website) have the errata included, though.