Servoy 3.0 Beta 2

Classic Servoy
12

application.output('SelectedTabFormName: '+elements.main.getSelectedTabFormName());

Do you see getSelectedTabFormName() in the method editor?
It is depricated you should use:

elements.main.getTabFormNameAt(elements.main.getTabIndex())

depricated stuff are not supported anymore in the webclient. So you have to use the new onces.