VBA Developers Handbook, 2nd Edition. questions on procedures and functions

Also, you don't want to be breaking encapsulation like that, you should be passing the UserForm object into the class. Oh, and don't use the default instances of user forms, ie. Never use NameOfUserForm.Show

You should be using them properly:

Dim uf As btn_Gen_uf2
Set uf = new btn_Gen_uf2

uf.Show

The default instances won't always be what you expect them to be