Hi
I had this with my LO - he turned 1 yr and then he would wake at 3.30 am chatting away for an hour.
I posted on this board and I had to look at my nap times. Does you LO always sleep for a full hour in the afternoon as our problem was overtiredness. He would sleep longer in morning and about 40 mins - 1 hour in afternoon but he was getting overtired by bedtime. I also found that he would get tired easily at 1 year as he had just started to walk etc etc.
I made the am sleep shorter 30 mins and extended the afternoon sleep to 1hr 30 mins sometimes 2 hours and put him in bed a bit earlier and he got back on track.
Lots of posts under this board deal with this subject as the transistion from 2-1 sleep seems to cause all sorts of problems!
Emma