http://www.cfr.org/content/publications/attachments/47.pdf
Read it and you will realize that to create conditions for a free & impartial plebiscite, Pakistan govt was to withdraw all tribesmen who had entered for the purpose of fighting and prevent any intrusion into the state of such elements and any furnishing of material aid to those fighting in the state.
Obviously, Pakistan did not do it and infact is still supporting intrusion into J&K and also furnishing material aid to the terrorists fighting in J&K.