Accessing foobar using this method was never supported. If you want to access foobar you should be doing it through supported interfaces, ie the command line or a plugin. There are multiple plugin's out there that supply a defined interface into foobar, off the top of my head, these names may not be exactly right, foo_mirc, foo_command, both do. All the developers have stated all along that accessing the fb2k window through the class name could break at anytime, and was not a suported way to control the app.