Microsoft is releasing a security update for the Windows 10 9879 preview build today that it knows will not install if a user's PC also has a version of its Office software suite in place on their hard drive.
In a series of messages on his Twitter account, Microsoft's Gabriel Aul admitted:
" ... we just made a tough call after working through the night that I thought I should share with you. We have a security update going out today, and the installer fails on 9879 if Office is installed. Rather than rolling a new fix (losing several days in the process) we're going to publish it as is. The workaround is painful: uninstall Office, install the hotfix, reinstall Office. Sorry. We're working hard to fix."
Aul also said that there will be three updates for the Windows 10 preview build today. Two are security patches, while the other is to fix "an HDD failure affecting some people". There is some light at the end of this tunnel; Aul said that users should try to install the KB3022827 update first to see if that will work for them before using the Office workaround. He stated, "It will work for many, no harm if not."
Source: Gabriel Aul (Twitter)