"...vous pourrez programmer votre combinaison personnelle quand vous arriverez ici." (recommended answer)
"...vous pourrez programmer votre combinaison personnelle quand vous serez arrivés ici." (marked incorrect)
While I do realize that the construction is covered at a higher level than this writing exercise, I was curious if the second sentence is grammatically or situationally incorrect? Or maybe just not preferred?
Merci!