Try with having same names for the buttons:
| | <div class="button_div"> |
| | <input name="Outcome" type="submit" value="Approved" id="Outcome" class="buttons" /> |
| | </div> |
| | <div class="button_div"> |
| | <input name="Outcome" type="submit" value="Rejected" id="Outcome" class="buttons" /> |
| | </div> |
Make sure that you have proper properties (process variables) defined and if that is user task is that you correctly map task input (given on the form) to the process variables - this is done via data output association.
HTH