2001 Pontiac Grand Am Brake Lines

I am wondering why you took the brake line loose in the first place. A normal working caliper and brake lines would not need you to break the line loose. But back to your leakage question. It is possible that you could have cross threaded the connection. But first I need to ask if you changed the brass washer with a new one when you reconnected the brake line? Did you make sure that the washer was good with no marks and truly in place? If not then that could be why it is leaking. That brass washer acts as a gasket.