We can conclude from the passage that Ivan had to look for a new position because …………

Ivan Greganti had greatly impressed the General when he suddenly turned up for an interview. He had more than enough qualifications with certificates to prove them and he had five years' experience working for the late Colonel Keller. Indeed, the Colonel had often sung his secretary's praises before he had been killed suddenly in combat, the previous month. Within the first week of Ivan's working in the General's office, he excelled at all the duties required of him. Despite his refusal to wear a suit, Ivan's system of sorting documents was so efficient that he accomplished twice as much work in half the time it had taken the General's past secretaries.