General: Sudoku

Does a Sudoku puzzle have a unique solution? Given that the books come with a answer key, one would assume they do. However the above puzzle given to me by the RadioShack Sudoku game seemed to have 2 possible solutions. The 2 and 6 could be flipped to dish out two perfect solutions. What bugs me is that, if there are two solutions then there could be more. So, is it a buggy Sudoku generating programs, or a norm?

Thanks, Akhil for pointing a error in the solution, here is the corrected copy