peterさん、

the pdf has been uploaded and you can re-download it now.

kore wa kantan ja nai hon desu is grammatically possible.
so it would not be a mistake to say it,
however, it’s not natural.

the natural way to make a na adjective negative is to use it as a predicate, so:

kono hon wa kantan ja nai desu.

that would be the best choice when dealing with -na adjectives.

hope this helps!

No I didn’t- so thanks for that.

But that still doesn’t make it clear that na should be dropped.

To labour the point it’s not clear whether it is:
kantan na ja nai hon desu or kantan ja nai hon desu

It is a hole in the grammatical explanation.

It gives as an example kore wa kantan desu -kore wa kantan ja nai desu but only gives kono hon wa kantan na hon desu.

There is no mention of what happens to na and you might think that it stays in place.

Check here:

http://www.japanesepod101.com/forum/viewtopic.php?t=3030

I have asked the question previously. There does not seem to be an answer.
What people who are capable of writing kanji are doing with basic lessons is beyond me.

Maybe Norman who posted just above can let us know.

あまりmeans NOT often
あまり魚は食べません。i do not eat fish often
since amali means NOT often. the sentence will be in negative form/and the paticle will be wa.

時々means sometime
時々魚を食べます。i sometimes eat fish
since there isn’t any “NOT” so it will be in positive form and teh particle is WA.

全然means NOT at all
全然魚は食べません。i eat fish NOT at all(direct translation, which is: i never eat fish)
there is NOT, so the sentence is negative and the particle is WA

hope this will be better

Nicholas L. さん
Thank you very much for your feed back.