The correct option is E No error
There is no error in the given sentence, as the words "not only...but also" is a correlative conjunction that presents two related pieces of information. Both these pieces are presented by the speaker as surprising or unexpected, the second one "to work as hard as the other patrons" being even more surprising than the first "He was ... expected to contribute funds to the project". "Not only" is crucial to the sentence, as it means 'apart from this', referring to the first piece of information, that the person was expected to contribute funds, which was unexpected, and apart from that he was expected to work as hard as the others as well, which is even more unexpected. Hence, there's no error in "not only", we don't choose option A. "But" is necessary to complete the meaning of the sentence, 'but' along with 'also' refer to the addition of the second clause "to work as...patrons". Hence, option B does not have an error, so we don't choose it. 'As' is a conjunction in the context of this sentence, and is used twice "as hard as" to refer to the manner of hard work by the patrons. "As...as" is a correlative conjunction that refers to the equality of work to be done by the person 'he', his work should be equal to the hard work by "the other patrons". Hence, option C has no error, so we don't choose it. 'Other' is an adjective that modifies the noun "patrons", excluding, or apart from the person "he", suggesting that he is also a patron, but is spoken about as an individual, and he's compared to the rest of the patrons in terms of hard work. Hence option D does not have an error, and we don't choose it. Since the sentence does not have an error, we choose option E.