Can the Essentials Berserker use Martial powers while they are in Berserker Fury?

There is one line on page 44 of "Player's Options: Heroes of the Feywild" that says "Additionally, since you can use martial powers only when you are not under the influence of your Berserker Fury, you should consider multiclassing into one of the Strength- or Dexterity-based martial classes and picking up or swapping in a power from that class."

Since not using Martial powers while in Berserker Fury is not mentioned anywhere else, is this just a typo or is it a rule?

It is a typo.

The only rule mentioning martial powers in relationship to your Berserker Fury (page 42):

Some of your powers, such as your barbarian martial at-will attack powers, gain additional benefits, as noted in those powers.

• Thanks. Since I'm perma banned from the WotC forum and therefore can't contact their support, can someone who reads this report this typo? Thanks. – Lokiare Jan 19 '14 at 14:22

I don't think it's a typo, I just think it's poorly phrased and a bit misleading, leaving the emphasis open to interpretation.

If you read the line as,

"you can use martial powers only when you are not under the influence of your Berserker Fury"

then it appears to refer to the fact that if you were to use a primal power (which is natively your only other option), it would trigger your fury. But then it immediately goes on to suggest MCing and power-swapping, at which point (stat array pending) you could just as easily poach divine or arcane powers, should you want to stay in defender-mode forever.

And given how incredibly silly that all is, it is easier to just read it like you have,

"you can use martial powers only when you are not under the influence of your Berserker Fury"

which is pointedly false. So I think they meant the first emphasis, but didn't really think any of it through (as is the issue with so much of the later Essentials content).