Answer:
The answer to your question would be that the type of error in the sentence above is a case mistake.
Explanation:
In English, the noun following a preposition is defined as the object of the preposition. Nouns do not change its form whether they function as subjects or objects but pronouns do. There are nominative (I, he, she, they, we) and objective pronouns (me, him, her, them, us). Those which function as objects take the objective case. In this case, the pronoun following the PP of takes the objective case, so it should be us, not we.
