Why?

Why? 各位大虾：帮看看，下面一段程序运行时提示“invalid  use of property" why? thanks! dim ff   as mapxlib.featurefactory dim newftr as new feature dim ftr1, ftr2 as mapxlib.feature dim ftrs as mapxlib.features dim lyr as layer dim i as integer set lyr = map1.layers("try") set ftrs = lyr.allfeatures for i = 1 to ftrs.count if i > 1 then ftr1 = ftrs(i) ftr2 = ftrs(i - 1) set newftr = ff.combinefeatures(ftr2, ftr1) newftr.update end if next