[eluser]gtech[/eluser]
seriously search the forums, when I am stuck I search the forums and usually someones already asked the question... scroll down 23 posts you will find someones asked this question today already
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as sikkle suggests the answer is don't call across controllers, it goes against MVC design.
1)create a base controller with common functionality and then extend it (inherit).
2)create a library / helper function and call the function from both controllers.
3)move common logic into the model.
good luck!