http://www.h-online.com/security/news/item/Avira-incompatible-with-Windows-8-and-Windows-Server-2012-1743293.html
Apparently, the problem will only be fixed by the company in the first quarter of 2013. Avira says that “significant changes to the operating system platform” of Windows 8 and Windows Server 2012 are the reason for the incompatibility.
Thanks avast! for doing the hard work before 
Hi Tech
I’m just amazed that Avira seem to be so blasé about it.
So yes, thanks avast! but at the same time, until any/all remaining Win8 issues with avast! 7 are resolved, it might be wise not to say too much, too widely about this (not that I think you have done so in this post), lest we be seen to be throwing stones while also apparently residing in a house made of optically transparent silica. 
They, and Avast to a far lesser degree, better get things fixed fast before too many just start relying on the improved Windows Defender and forget completely about 3rd party solutions.