Thanks for the update indeed! After uninstalling everything and reinstalling the new drivers and tools it finally works for me, too.
I still have a major problem though, but that does not seem to be specifically Tobii-related but rather a Windows 8.1 / graphics driver issue, since it happens sometimes with other apps, too: whenever I have a second screen attached to my notebook the Tobii app will crash. So in case anyone has similar problems I recommend to try running/installing Tobii without a second screen attached.