Just moved into a new house a few months ago... (4 level split with 3rd level on a concrete slab). On the 3rd level in the corner of our family room there was ice on the drywall (very cold out -45 with wind chill). Was wondering if possibly vapour barrier was not installed correctly because I know for a fact there is insulation behind the wall? Another person mentioned because we had several large blankets stuffed in this corner that is why the ice formed between the wall and the blankets... any truth to this?

Yes I would suspect the vapor barrier was not there Or the insulation was not complete. The other player to help or the cause was couple of blankets because that spot was denied the room heat and the thermal break was between the cold inside the finish wall and the blanket and that became the vapor barrier. The extra cold with wind also could have contributed to penetrating the insul in the corner If you have an outlet on or near this wall take the cover plate of and check for any cold air flow this would help determining if there is any cold air flow in the wall. If the insulation was subjected to a 5% moisture content its now lost about 95% of its insul properties. See what happens with the blanket away and feel that wall area as opposed to other outside walls. The first worry hear did the insul get damp in the wall. Of course to answer that would be poke a hole or get a moisture reading probe and poke a smaller hole.

I agree with 21boats explanation. By putting blankets againist the outer wall you created a new insulated area with no vapor barrier. The room moisture was able to condensate on the wall surface and the blanket kept room air from circulating heated air. I think your insulation under the dry wall is still fine since no additional moisture was allowed to penetrate the barrier, it will once you poke that hole so don't.