"She was looking for a book when I arrived."
Translation:Elle cherchait un livre quand je suis arrivée.
Why is "Elle cherchait un livre quand je suis arrivé" not acceptable?
Am I not allowed to be male? Or does arrivée have to agree with the first subject for some obscure reason?
It sometimes takes a few hours (up to two or three days) for the changes to actually show. Unfortunately, there's not much we can do about it except wait and be patient...
But if it still doesn't accept it after the 5th of April, please take a screenshot and post it here.
Because arriving is not an ongoing action, it's something that happened a single completed time in this context. A lot of the imperfect is like this, you get all the imperfect describing all the things that were going on until some specific thing happened and that specific thing which has a definite end is in the passé composé
and what about " Elle cherchait un livre quand j'arrivai", simple past is the same as passé composé in that case ?
Yes. Please don't use "pour" with "chercher" to mean “to look for”. That preposition “for” is only in English.
Why is "Elle cherchait un livre lorsque je suis arrivé." not correct?
I must admit I am not quite sure about the correct usage of lorsque, but can't it be used as "when" outside of questions?