Gerund phrase and infinitive phrase

[infiniteone]

There are two sentences.

A. It is important to study each subject every day even if it is just a little bit.

B. It is important studying each subject every day even if it is just a little bit.

Is there any difference in meaning between the upper sentences?

One man said that when someone uses gerund phrase instead of infinitive phrase with the empty subject, it can refer to kind of unusual situation or acting. Is that right?

[mmasny]

I can't help you with these, but I can give you two sample sentences showing that there can be a difference in meaning between a gerund and an infinitive.
I stopped smoking.
I stopped to smoke.

The first means that you didn't smoke any more. The second means that you stopped doing whatever you had been doing before in order to smoke.

[infiniteone]

sorry, your reply does not correspond with my question.

[mmasny]

I'm sorry too. That's how I undertstood this:

One man said that when someone uses gerund phrase instead of infinitive phrase with the empty subject, it can refer to kind of unusual situation or acting. Is that right?

[Raymott]

There are two sentences.

A. It is important to study each subject every day even if it is just a little bit.

B. It is important studying each subject every day even if it is just a little bit.

Is there any difference in meaning between the upper sentences?

One man said that when someone uses gerund phrase instead of infinitive phrase with the empty subject, it can refer to kind of unusual situation or acting. Is that right?

Sentence B is not grammatical. A is. That is the difference.
I think mmasny was trying to illustrate to you that you cannot substitute one form for the other without risking i) a change of meaning or ii) an ungrammatical sentence.

[infiniteone]

Sentence B is not grammatical. A is. That is the difference.
I think mmasny was trying to illustrate to you that you cannot substitute one form for the other without risking i) a change of meaning or ii) an ungrammatical sentence.

I think Sentence B could be grammatical.
I have seen many sentences including gerund phrase like Sentence B on newspapers like these sentences : "It's difficult getting food and water through to earthquake survivors", "By all accounts, it's difficult doing business in China but surely it's not difficult to do the right thing. "

[mmasny]

Grammar is not always logical. It's shaped by the custom. You can't always put a word somewhere in the sentence because others (even similar) can be put there.
I think here's the answer to your question:
It's + adjectives + doing

I didn't answer it before, because even though I've never heard a sentence like B it didn't seem very wrong to me. As it probably was in your case. But being told the answer by the experts we have no right to argue. They simply know what people speak and write like. And this is the language - what they speak and write like.