I almost included in my last post that I would have guessed you had put a while loop in the subVI with a front panel stop button.
When you do something like that and don't make the front panel of the subVI visible, then there is no way to click the stop button and the subVI will just run forever until you click the abort button. Also, basic programming says that a function will not return a value until the function finishes. Since the subVI never stops, you never get a value back from it. The simplest thing for you to do right now is to put the small amount of code of the subVI in your main VI. The main VI you created doesn't do anything anyway. Your main VI should have the while loop.
