Haven't been able to find this issue elsewhere, except during the earlier variants of the developers beta. Have a 2012 i5 Mac Mini with a 120gb SSD and 500gb HDD using the iFixit kit. I've been running the public beta since release on the SSD (wherein Avast had been working fine), but yesterday I installed the dual HD setup, did a fresh install of Yosemite on the SSD, then updated back to 15A243d public beta and installed Windows 8.1 on a Bootcamp partition on the SSD, leaving the HDD with one Mac OS Journaled partition and one NTFS partition. Both El Capitan and Windows 8.1 see all drives and partitions just fine. Beforehand, when Avast worked, I had installed it originally on Yosemite, and the app had rolled over through the El Capitan updates. This time, however, I tried to install it after I updated to 15A243d – no go. Fails each time it tries to validate the packages after running package scripts, right near the end of the install. Also, unlike on Yosemite, it won't let me choose whether I want to install on a specific disk or for a specific user; it forces me to choose to install for all users of the Mac. Anyone know what might be at fault here?