Yup I can confirm that the latest avast beta dont compatible at all. It manage to install and run on Windows 8.1 Preview but open shutdown after restart you will see big problem. Error will appearing without stoping and after the shutdown, Windows 8.1 will not be able to boot up pass the login and password.

For MAC user beware that Windows 8.1 also will effect your mac and cause you to remove Windows Partitions.