Hello Sasha. Tricky, that one. Your logic is sound, but I don't think it sounds idiomatic when you use the simple past. In this sentence, with a few tweaks, Andrew is the cause of the employment-related ennui: - After Andrew came into my life, I began to move from one dead-end job to another, without much idea of what I really wanted in life. In this one, he may actually be the person who saves the writer from the sorry state of affairs: - When Andrew came into my life, I was moving from one dead-end job to another, without much idea of what I really wanted in life. So in relation to the test, I would say both are possible, grammatically; but the second -- the past continuous form -- makes more sense in terms of the semantics. Take your pick. ;-)

I agree with Gareth - both meanings are possible but different and that the past continuous is more natural. This is a narrative and the writer seems to be setting the scene connected to a particular period. This suggests the past continuous. If there was a sequence in the past simple, the words "once" or "as soon as" would better indicate this than "when", which is a more general idea.