Obtaining AutomationId from WPF applications

In my case I am interested in the VerticallyScrollable property of a UIAutomation object for a WPF application. I tried modifying the sample provided in Tanya's post after proving I could successfully obtain the AutomationID. However, I am sure I am making an obvious mistake:

(Using JavaScript...)

var SV, AutomationIdProperty, AutomationID;
SV = Sys.Process("MyApp");

AutomationIdProperty = SV.AppDomain("MyApp.exe").dotNET.System_Windows_Automation.AutomationProperties.AutomationIdProperty;

AutomationID = MyWPFObject.GetValue(AutomationIdProperty);
Log.Message(AutomationID);   //Success!!

AutomationIdProperty = SV.AppDomain("Zetta.exe").dotNET.System_Windows_Automation.ScrollPattern.VerticallyScrollableProperty;
AutomationID = MyWPFObject.GetValue(AutomationIdProperty); //Fails here with error: "The parameter is incorrect"

Log.Message(AutomationID);