While there is no law that prevents the President and Vice-President from being from the same state, the Constitution states "The electors shall meet in their respective states, and vote by ballot for two persons, of whom one at least shall not be an inhabitant of the same state with themselves." This means that the electors for the Electoral College from their state could not vote for both persons on the same ticket which in all likelihood would result in one of the parties losing. In the case of the Vice-President not getting those votes, the VP would be decided by the Senate.