Problem filling a Spinner

I have a problem filling a Spinner, I've tried to add the elements both with the Add(String) and Add(List) methods. Here's the source code:

'Activity module
Sub Process_Globals
'These global variables will be declared once when the application starts.
'These variables can be accessed from all modules.
End Sub
Sub Globals
'These global variables will be redeclared each time the activity is created.
'These variables can only be accessed from this module.
Dim spUser As Spinner
Dim btnConfirm As Button
Dim btnCancel As Button
End Sub
Sub Activity_Create(FirstTime As Boolean)
Dim UsersList As List

Activity.LoadLayout("Login.bal")

UsersList.Initialize()
UsersList.Add("SQnet")
UsersList.Add("Admin")
UsersList.Add("MyUser")

spUser.Initialize("spUser")
spUser.Add(UsersList)
End Sub
Sub Activity_Resume
'
End Sub
Sub Activity_Pause (UserClosed As Boolean)
'
End Sub
Sub btnConfirm_Click
Activity.Finish
End Sub
Sub btnCancel_Click
Activity.Finish
End Sub

Thanks in Advance
Gianfranco