Android Question Problem with Google AdView after update to B4A 4

Hello, I have an app that works good in B4A 3.82 but when I run it in B4A 4 I get an error in this line of code:

Activity.AddView(Adbox, 0dip, 100%y - height, 100%x, height)
Adbox.LoadAd

it says that doesn't find class file for com.google.android.gms.ads.AdView
but file is there where indicated on top of the app...
Anyone knows what can be wrong?
Thanks for your help
Massy