Inaccessible_Boot_Device Error Upgrading to Insider Build 16215

I have been getting used to having to apply workarounds to get the Insider Preview Builds installed. On one of my systems, after months of frustration, I finally figured out I had to remove the WLAN PCI card, upgrade then re-install it. That has been consistent for some time now.

Build 16215 was released and my SurfaceBook upgraded without issue (though there have been some "possible" bugs I've noticed) but 2 of my other systems - an ASUS Desktop and Lenovo Edge 2/1580 running Build 16199 have both refused to upgrade. The ASUS would throw an inaccessible_boot_device error on a green screen and the Lenovo would just fail during the upgrade and rollback.

This morning I started browsing online looking for solutions or if others experienced the same issue and found this.

The majority of users had SSD's that they felt were the cause of the issue; but the 2 systems I was having issues with were running a standard platter based hard drive and the other a hybrid. After looking through the posts I noticed a user or two stating that Acronis True Image, once removed, allowed the upgrade to proceed.

I decided to peek through my program list and noticed I was running Easeus ToDo Backup Version 10 and Recuva which I felt might possibly create an issue. I removed both and the install proceeded and completed relatively quickly with no errors. My bet would be on the Easeus ToDo application causing the upgrade issue due to drivers and services it installs for imaging. Hopefully this helps someone. If you have the same issue and managed to fix it - please share your fix.