WinSetupFromUSB Failed… | John Fender Blog:
grubinst.exe could not make a backup of MBR
"To fix the GRUB error it's simple, don't use the RMPREUSB as requested. Use the old HP format tool (you can found it in the files/tools/ dir as HPUSBFW.EXE) and format the key in NTFS. Now it will work. Done with my SanDisk 16 GB bey."