L.P.
CIO actually produces/exaccerbates separation anxiety in some kids. My son was one of those: we were desparate for sleep when we finally tried the Ferber Method with him at around 10 mos. At that point he could start the night in his own bed (although it took a lot of work to get to that point) but when he woke up a few hours later he couldn't resettle.
It was a disaster. We were dedicated for a week, at which point we realized it was just making things much worse, not better. He started to get anxiety about going in his room, would no longer go down at the start of the night etc. So we stopped and started over from scratch again.
We had to go back to rocking/bouncing him to sleep for a week or two and then, once his anxiety decreased, we were able to sit with him in his room while he went to sleep in bed. Gradually, we could decrease the amount of time we spent sitting next to his bed until we could finally put him in bed and walk away while he was awake with no crying.
According to the sleep specialist (yes, he was a tough case) sleep is a neurological process that develops at it's own rate for each kid, and even Ferber has begun to realize that CIO only works for certain kids in certain situation. For lots of kids in makes things worse.
I would recommend working on soothing him back into starting the night in his own bed. Once he is comfortable starting the night there you can adjust his schedule so that he begins to sleep for longer stretches. What we finally had to do (under the direction of the specialist) was the same thing our friends (who traveled to Ferber's sleep lab for their son) did: around 12 mos gradually push back bedtime and keep a strict wake-up time to consolidate night sleep, and gradually restrict day-time sleep to one nap in the middle of the day.
Initially, this meant keeping our little guy up later and later until he was going to bed at 10pm (ugh) and getting him up at 6am, and pushing back nap until 11:30am. It was atough, but he finally began sleeping through the night, and because we'd worked to make sure that we went to bed in his room, when he started sleeping through he stayed there. It was sweet, sweet relief for us all!!
Good luck! Sleep issues are hard and there's no good, quick fix that works for every kid.