Windows Longhorn build 4042 (main)

Windows Longhorn build 4042 (main) is a build of Windows Longhorn. This build was compiled four days before the Lab06_n compile, and as such, is technically a Milestone 6 build. Prior to being shared, UX.Unleaked had a post with three images from this build. Later on 23 January 2020, this build was listed on a thread by the blog's founder Grabberslasher to be released to the BetaArchive FTP, and was released in the twelfth and final set of his 33 Longhorn/Vista builds on 4 February 2020 along with build 4082, build 4087 and build 5492.

Setup
Setup is mostly similar to previous builds of Longhorn.

Changes

 * The Windows Media Player tile now fully functions.
 * Safe Mode now fully functions, after being broken in build 4032.

Bugs

 * Even if the Windows Media Player tile fully functions, the CPU usage will increase dramatically.

Desktop Composition Engine

 * The full Aero framing is not functional in this build.

Installation

 * On certain hardware, setup will not terminate correctly. The theming service will be missing from the operating system and a zero-day activation problem will occur.
 * On some computers and virtualizers, this build can't be installed from CD boot as is. You must use the WinPE from a different build, or upgrade from a previous build.

Upgrade

 * It is currently not possible to upgrade to this build. After the second reboot, Windows will corrupt the registry and will fail to boot, causing the error   when upgrading from most builds prior to this one.
 * When upgrading from 4029,  terminates with a critical error, and the system will become stuck in a bootloop. The only workaround is to reinstall Windows.