Btw, everyone, I’ve gone to Microsoft about this as well, at the following thread; and, so far, they haven’t been able to come up with any resolution either:

http://answers.microsoft.com/en-us/windows/forum/windows8_1-windows_install/update-to-81-wont-work-because-of-avast-antivirus/63268a12-63e9-4685-8abb-1ad09b24c953?tm=1383249388208&rtAction=1383521370396