1. Answer: The error in this sentence lies in the incorrect use of the causative verb have. As a causative verb, the correct usage of have is have sb do sth, that is, have is followed by an infinitive of the verb without to to serve as the direct object. The original sentence is corrected to: He had us clean the room the whole afternoon. He had us clean the room the whole afternoon.
2. Grammar: Verb infinitive is a common non-predicate verb in English. Although it cannot serve as a predicate verb, it can play almost all sentence components except the predicate, such as subject, predicate, object, adverbial, attributive, complement, etc. Generally speaking, the infinitive of a verb is composed of "to + the original form of the verb". But in special cases, the marker word to of the infinitive of the verb is often omitted. These special cases of omitting to include the following: ① After come and go in spoken language. ② Compare the structure than behind. ③ After causative verbs and sensory verbs. ④ behind the verb help.
3. Example: verb inequality with to omitted
① Go fetch some water. Go fetch some water.
② I'd rather stay here than go at once. I'd rather stay here than go at once.
③ I saw some old people dancing on the square.
④ Planting trees can help make our city cleaner and nicer. Planting trees can help make the city cleaner and more beautiful.