 Nietzsche’s formulation (“that delusion and error are conditions of human knowledge and sensation”, and that this insight “comes to us through science”) suggests that the specific error theory he has in mind is rooted in the Kantian and Schopenhauerian theories of cognition, perhaps as developed in more naturalistic, psychologically-inflected form by later neo-Kantian and positivist thinkers. Those views would entail that the basic conditions of cognition prevent our ever knowing things as they really are, independently of us (see Anderson 2002, 2005; Hussain 2004; and the entry on  Friedrich Albert Lange).  But while those are the immediate allusions, Nietzsche also endorses more general ideas with similar implications—e.g., skepticism against any thought (be it of the theological/metaphysical, or Hegelian, or more modest, third Critique oriented sort) that the world is purposively suited to fit the needs of our cognitive faculties.