Need to replace screws

Hello - My Galvalium roof is leaking in several places. The panels were screwed into the purlins. I'm thinking that the screws were too short, as many of them are not coming all of the way through the wood. There are others where just the tip of the screw comes through. I'm wondering if the screws are backing out because they are not long enough. Is it likely that replacing the shorter screws with longer ones will solve the problem? Thanks, Dan