If the same Noun is used before and after the preposition, then at both the places, the Noun is used in Singular Number and verb should also be singular.
Example: He made / attempts after attempts / but failed. / No error
Explanation: In the above sentence there is an error in the second part of the sentence as the structure of the sentence is:
Noun + Preposition + the same Noun repeated
and in this type of structure, singular noun is used at both the places.
So, ‘attempts after attempts’ should be replaced by ‘attempt after attempt’.
Hence, the correct sentence should be:
He made attempt after attempt but failed.