When you can't select the stroke alignment, it's usually because you or the person that created the object you're trying to outline, created a line segment instead of a complete or closed path. Using the pen tool, hover over the anchor points. When you mouse over the line between anchor points, you'll see a "+" sign, offering you the option to add an anchor point. Mouse over an anchor point and a minus sign should appear (option to delete anchor point) If you get a diagonal slash, however, you've found your problem. This indicates a line segment and not an anchor point. Simply hold the ctrl (command) key, deselect the object, then while still holding ctrl key, highlight the point that was found to be a line segment. Be careful to avoid selecting other points. Then, hit ctrl+J to join the points and close the path. Now you will be able to align the stroke anywhere you please.
So, the short answer is, you're not working on a closed path. Find the open segment, close the path and you're in business.