Weird substr issue

1 

var pinDate:String = new String(); 
pinDate = startDates[j]; // Fake value here like "12/12/2009" will work.
trace ("pin's date: "+pinDate); // returns in form of 09/12/1989
var pinYear:String = new String();
pinYear = pinDate.substr(6,4); // not working!!!!!!!!!!!1!!!!!!

Won’t grab my substring.
I’ve tried using <i>substring</i> and a bunch of other stuff. Still returns undefined. Using Flash 8. startDates returns “09/01/1880, 12/12/1899, etc.” Any ideas??