Answer: The type of pronoun error in the sentence is B. case.
Step-by-step explanation: In English, personal pronouns have three cases: subjective, objective and possessive. Subjective case pronouns are used to replace the head of the subject or to accompany a noun subject. Moreover, a subjective case pronoun can also function as subject complement. However, when constructions such as "neither of" or "either of" are used in a sentence, they must be followed by an objective case pronoun. In that way, the type of pronoun error in the sentence "Neither of we boys was going to the ball game" is case because the pronoun that should be following the construction "neither of" is "us" (an objective case pronoun) and not "we" (a subjective case pronoun).