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

<img src="images/post/smile/dvbbs/em09.gif" />