I am running a 2010 MacBook Air upgraded to High Sierra. With the upgrade, I was no longer able to boot my Win10 Boot Camp partition. The partition is accessible in High Sierra as volume.
I used WinClone Basic to save the Win10 Boot Camp partition. I resized in Disk Utility to give unallocated space to the Win10 partition as an MS-DOS partition.
I restored the Win10 partition with WinClone.
Win10 attempts to boot but fails with “BOOTMGR is compressed” error message.
Per another post on this Forum used WinClone to attempt to “Make EFI Bootable”. WinClone lost in “Copying EFI Boot Files” and makes no progress.