What is the error in this sentence?

"Dr. Smith had argued that the cure for insomnia could be found in the seeds of apples, and although it was not true, he had made money giving lectures." This statement:

A. Includes a shift in tense
B. Includes a pronoun with no appropriate antecedent

We'll be happy to check your answer. Study this about verb tenses and sequence of tenses:

http://grammar.ccc.commnet.edu/grammar/verbs.htm#sequence

So, according to your link, the verb tenses for this sentence are appropriate. Thus, the pronoun "it" in the subordinate clause needs to be replaced with a more descriptive word or group of words like "his argument." Would this be true?

No...

When did he do the arguing? When did he make money? Which one happened before the other?

Okay, so it should be more along the lines of "he has made money giving lectures," in order to show that he currently possesses the money.

So ... he made the money and then he did the arguing??

Sorry, according to my lesson, my antecedent deduction was correct and your verb tense argument was wrong.

Too bad.

The past perfect tense is used incorrectly in that sentence.

Could you please explain to me how it is used incorrectly? You aren't giving much reasoning behind your answer, you're just giving me an answer.

He argued in the past but then had made money puts it at a prior time to arguing.

The purpose of the Past Perfect Tense (had made) is to show an action in the past tense but prior to another verb in the past!

Writeacher was asking you WHICH happened first.

Sra

B. Includes a pronoun with no appropriate antecedent