Am I missing something here? Since I installed the Windows 10 Tech Preview it keeps telling me that I cannot re-install Avast due to ‘compatibility issues’ ?? As it exhibits the same problem with my (preferred) firewall software am I to assume that Microsoft have altered something so that only their antivirus/firewall programs work?
Welcome to the forum. 
You’ll find the problem already being discussed at:
https://forum.avast.com/index.php?topic=156141.msg1175873#msg1175873
At the moment there isn’t any answer.