The response code is 161.
I’ve had it happen to my own account and I am able to follow the same user within twitter.com. Looking in my database, some members appear to still be able to follow people. Nothing is automated, my app just allows users to find accounts to follow by searching via keyword or searching through mutual friends. We limit them to 300 per day which is less than the 1,000 limit from twitter that I saw. Our current feature set is similar to crowdfireapp.com to be honest. Keeping track of their reach (follower count), new followers, new unfollowers, etc…