Identify the part of the sentence that contains a grammatical error: 'Both (A) / Raghu as well Raminder (B) / should be rewarded (C) / for their brave act. (D)'

Find the part of the sentence that contains a grammatical error: (1) Scarcely had the newly appointed Director of Intelligence assumed her post / (2) when a sophisticated cyber-espionage campaign was detected / (3) within the high-security servers of the national defense agency, / (4) prompted an immediate and total lockdown of all external communication channels.

Find out which part of the following sentence contains a grammatical/contextual error: I congratulate you (A)/ on your success (B)/ in the examination (C)/ that never happened last week (D)