It looks like you are qualifying the control name with a Form name. Controls belong to Modules not Forms, you can see this in the right hand pane, so you should use the Module name as a qualifier if a qualifier is needed.
There doesn't seem to be much you can do with a Tab control, nothing on the device and on the desktop the only thing that seems to stick is the Font.
Obj1 is a Door library Object, Font is an ImageLibEx NormalFont.
Obj1.New1(False)
Obj1.FromLibrary("Main.tab", "tbc", B4PObject(2)) ' get the TabControl
Font.New1("Times New Roman", 10, 1)
Obj1.SetProperty2("Font", Font.Value)