B4J Question Multiple modal form

[AlpVir]

With B4A could, from a menu Activity, to toss many others. Well.
With B4J I not understand how it is possible. Sig !
I have a main form (MainForm) and the code :

Sub SKI_action
Dim mf As SchedaScialpinismo
mf.Initialize (MainForm)
mf.Show
end Sub

start the class SchedaScialpinismo. Allright

When I add the code in the MainForm :

Sub CREAVUOTO_action
  Dim mf As CreaArchivioVuoto
  mf.Initialize (MainForm)
  mf.Show
end Sub

to start the class CreaArchivioVuoto appears the error : Array expected

In both classes SchedaScialpinismo and CreaArchivioVuoto exists the sub :

Sub Show
  frm.ShowAndWait
end Sub

I do not understand the mechanism of interaction between the (possible) several form of a project.
I have read and I tried to apply the advice of Erel (https://www.b4x.com/android/forum/threads/modal-dialogs.34656/)
Thank you in advance.

SOLVED
Changing the line
mf.Initialize (MainForm)
(Sub CREAVUOTO_action)
in
mf.Initialize
everything seems OK.
I did not understand the reason !
Thanks and sorry for the trouble.
I am new with B4J.