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ありがとうございます。Could you explain why you use は　instead of が in the second correction? I thought it would be が because "I" is the understood subject and "grammar" is the direct object...

so if i included both it would be:
私はぶんぽうがすきではありません。。。
or is that wrong too?
if so, i have been doing a LOT wrong...

"私はＡは好きで（は）ない" is a common collocation. Also, you can write:
"私はＡが好きで（は）ない". The difference is difficult, but the basic meaning is the same here. (It is not always the same.)

soooo... is it alright to use が in that situation?

日本語のぶんぽうはとても難しいですよ。ぶんぽうがすきでわありません。。。
In this context, I think は is clearly better because you are talking about the Japanese grammar, the topic. The topic is indicated by は, not が. Morever, when I think with only one sentence, "ぶんぽうがすきでわありません。。。", は is better, because が generally means "the xxx of the class", so 文法が means "the (Japanese) grammar of the (Japanese) grammar"; however, there is no other "the (Japanese) grammars" except for sole "the (Japanese) grammar", so 文法が and 文法は indicate the same thing. In that case, は is usually used, because senteces without topics are generally unstable.

Okay thank you^_^ That made more sense than most of my textbooks could have hoped for.

どうもありがとう！

ありがとうございます。