We moved into our 12-year-old house last fall (in NY) and had all the bedrooms repainted. No nail pops were evident at the time. During the winter, nail pops occurred in 3 of the bedrooms on bot the ceiling and the walls - why would this occur after 12 years? Do we have a possible major issue on our hands (i.e. - rotted board, bad insulation)? Thanks!

The most frequent reasons for nail pops are;
1. Used wrong kind of nails
2. Shrinkage in the framing due to drying of the framing lumber. or use of limber with too high a moisture content.
3. Some sort of structural failure which causes movement in the framing.

Number 1 would have shown up early. Number 2 is a possibility. Number 3 also would most likely have shown up in the first couple of years.

Why it occurred for the first time after 12 years is a mystery, unless of course it has happened before and was repaired by the previous owner.

I don't know what your weather has been like up there, but if you have been experiencing either extreme drought or extreme rain, this can create enough soil instability to cause this due to foundation movement. It can also cause foundation slabs to crack.