Windows 10 Insider Preview 17063 announced on the 20th December 2017 has added a new restriction that unfortunately has caused the Macrium Reflect Changed Block Tracker (CBT) driver (MrCbt.sys) not to load at startup.
INACCESSIBLE BOOT DEVICE
So what's happened?
MrCbt.sys is a Windows kernel driver that follows a similar architecture to Microsoft's own Volume Shadow copy Service (VSS) driver VolSnap.sys. The style of this driver is known as 'Legacy' and there are several MS drivers of this type in the kernel stack, in all versions of Windows.