Can someone here help explain to me why this groovy macro code is not returning any values when run on an instance? 

I get back an SimulationResult from the .execute(parent, true) operation, but the .getOutputValues() method always returns an empty map. 

The Simulation API is really sparsely documented.

Browser browser = Application.getInstance().getMainFrame().getBrowser() // Get the Browser Object
BrowserTabTree activeTree = browser.getActiveTree()                     // Use that to get the active Tree
SimulationManager simMan = new SimulationManager()
for(node in activeTree.getSelectedNodes()) { // for each selected item in the tree
   parent = node.getUserObject()            // Get the user object (not the tree reference object)
    WriteLine("SimElement: " + parent.getName())
    SimulationResult result = simMan.execute(parent, true)
    values = result.getOutputValues()
    writeMap(values)
}

def void writeMap(Map inMap) {
	for(key in inMap.keySet()) {
		WriteLine(key.toString() + " : " + inMap.get(key).getName())
	}
}

// WriteLine
// Utility function to simplify writing text to the notification window    
def WriteLine(String msg) {
    Application.getInstance().getGUILog().log(msg)
    }