Man opens fire in Colorado movie theater

Could you provide a link to where it states it is illegal?

Keep in mind there are no laws to say if something is legal. There are only laws to say if something is illegal.

I can not find ANYTHING in Article 265 of NYS Penal Code (the one that deals w/ guns/firearms/weapons) that pertains to carrying of a rifle or shotgun in a concealed manner.
You WILL see laws that say it is unlawful to carry a loaded firearm unless you are licensed to do so, but here is NYS’s definition of a firearm:

  1. “Firearm” means (a) any pistol or revolver; or (b) a shotgun having
    one or more barrels less than eighteen inches in length; or (c) a rifle
    having one or more barrels less than sixteen inches in length; or (d)
    any weapon made from a shotgun or rifle whether by alteration,
    modification, or otherwise if such weapon as altered, modified, or
    otherwise has an overall length of less than twenty-six inches; or (e)
    an assault weapon. For the purpose of this subdivision the length of the
    barrel on a shotgun or rifle shall be determined by measuring the
    distance between the muzzle and the face of the bolt, breech, or
    breechlock when closed and when the shotgun or rifle is cocked; the
    overall length of a weapon made from a shotgun or rifle is the distance
    between the extreme ends of the weapon measured along a line parallel to
    the center line of the bore. Firearm does not include an antique
    firearm.