Change internal Captivate variables via actions

I would like to be able to increase the variable cpQuizInfoPointsscored by 1 using an Advanced Action. But if I use the Assign or Increment actions, this variable does not come up in the list and even if I type it in I cannot save the action. Is this not possible? It is listed in the IF part of a Conditional Action but does not show for the Else part, and not at all for Standard Actions.