The correct answer is D. No error.
The sentence “He has not been attending English classes since one month” is grammatically correct. The verb “has not been attending” is in the present perfect continuous tense, which is used to describe an action that started in the past and continues up to the present. The adverb “since” is used to indicate the beginning of the action, and the noun phrase “one month” indicates the length of time that the action has been taking place.
The other options are incorrect because they either change the meaning of the sentence or make it grammatically incorrect. Option A, “He has not been attending,” omits the necessary information about the action that the subject is not doing. Option B, “English classes,” is a noun phrase that is the object of the verb “attending.” Option C, “since one month,” is an adverbial phrase that indicates the beginning of the action.