Have you put the resistor in the right way round?
Also it depends on the quality of resistor, the end of it is marked Bronze, silver, or gold, and the charachteristics of each determine how accurate they are at that certain level ie; a 2kohm resistor with a bronze band will have a resistance of between 1.7 + 2.3 kohms, whereas a gold one will be very near 2kohm etc etc.... Not exact but you get the picture. Could be a determining factor though.
