General notes about “Windows XP Mode”
“Windows XP-Mode” is a special Windows Virtual PC image, which is only available for Windows 7. It was developed as a temporary solution to make old applications bootable which do not work natively with Windows 7.

Problem
The default FireWall installation of Avira in this particular XP-Mode makes the entire virtual machine unbootable. It turned out that this can’t be changed with an Avira-Fix, because the bug lies in the architecture of this special virtual XP-Mode.

Solution
The Avira setup routine has been refined and recognizes attempts to install Avira in the “Windows XP-Mode” image. Once that happens, the Avira FireWall won’t be installed so that the Virtual Machine keeps running.

It is therefore not possible to use the Avira Firewall in this type of Windows virtualization.

Advice
Do not use this “Windows XP-Mode”, but rather a full virtualization with software, such as VMware, VirtualBox or Windows Virtual PC. Here you should be able to install and use the Avira FireWall without problems.