FYI: After getting this alert for 2 days when trying to reply to a message from a fellow member, I finally figured out that the person I was replying to had set up her profile to not allow other members to contact her. If I try to send her a message outright, I get: "This member has chosen to not be contacted. We're sorry. You are unable to reply to (member name) because they have currently chosen not to allow other members to contact them. You may want to check again later in case they change their settings"

I'm just posting this in case other people run into this situation. Seems to me that Ancestry.com should change the initial alert message I got so that it didn't take me so long to figure out what the issue was.