Question: I don't know which page in the book "Practical English Usage" I can learn about the usage of "have problems V-ing".

I try to look this usage up in "Practical English Usage" (Michael Swan).

Because I do not understand a sentence like the following one.

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> "Students find it so easy to blame others or complain about their difficult situation when they have problems preparing for the IELTS test."
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The structure of the form "*have problems V-ing*" is not clear to me.

I hope somebody bring answers to these questions.

Is it correct to say 

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> "...*have problems* **of** *preparing* for the IELTS test."
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or 

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> "...*have problems* **to** *prepare* for the IELTS test."?
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or

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> "...*have problems* **to** *preparing* for the IELTS test."?
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What is the difference between those three sentences in meaning?

How do I look this usage up in "Practical English Usage" (Michael Swan)?

Answer: 
Linguists would say that "The noun *problems* may take a subjectless gerund-participle clause" as a complement; but that's not a *Why*, it's just a name for the fact that that is how we say it. 

To say that *Students have problems preparing ...* means that students find some aspect of preparing difficult. 

You may also speak of problems ***with*** preparing, but that usually means having some (unspecified) objection to *preparing* itself. And you may speak of problems ***in*** preparing, but that usually means problems of some (unspecified) sort encountered while you are preparing. 

You may encounter *problems **of** preparing*, but the preposition *of* introduces a specification of the problems, such as "the two problems of finding the error and repairing it".

Neither of your suggested alternatives with *to* is idiomatic.
And we can substitute a number of analogues for **problems**:

Do you have difficulty walking?

Do you have pain standing up?

Do you have trouble sleeping?

Do you have shortness-of-breath climbing stairs?

Do you have qualms doing that?

P.S. And they don't have to be problems:

Did you have a good time visiting them?

Do you like eating there?

Do you miss going there?