After further investigation, this code does work. The problem I was having was trying to rebuild a locator which was moved from ArcSDE 9.x to our Development ArcSDE 10.x database. ArcGIS 9.x Locators must be recreated in 10http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//00250000001w000000.htm%20