I have a 1-year old son that has a lot of trouble sleeping at night. From the day he was born until about 10 months old he had to be rocked to sleep. At 10 months old we sleep trained him using Ferber method and it worked. At bedtime we would hold him for a while, read a book, pray, etc., then put him into his crib. He would cry for a very short time, sometimes less than a minute, then fall asleep. Throughout the night he would seldom wake up, maybe one time at most, and even then he would fall back to sleep by himself. 

When he turned 1 year old this method only had a 50-50 chance of working. Now when we put him into his crib he would cry for a long time, could be up to 15 minutes or more. And when he cries a long time, there's a good chance he would puke, and then chaos ensues. During the night he wakes up frequently, 2-3 times, and need to be rocked to sleep again. 

Note that he has no trouble at all sleeping two naps during the morning and afternoon. We rock him to sleep at naps, and it's usually fairly effortless. 

I do not think he goes to bed hungry. We give him an 8 ounce bottle of fresh milk about an hour or so before bed time. 

I don't know what went wrong and I don't know how to fix it. Why did he revert back to previous state? Is there something about night time that scares him now that he's more developed? We have a small night light in his room. Thanks for your help.