Grub errors during UEFI dual boot for Windows 8 (can't find command 'drivemap')
Solution 1:
I had this issue as well. I followed the instructions here:
https://wiki.archlinux.org/index.php/GRUB2#Microsoft_Windows_installed_in_UEFI-GPT_mode
The curveball is that I could not edit grub.cfg directly, as on my machine it is generated by the grub-mkconfig command. I added the 'menuentry "Windows ..." { ... }' to /etc/grub.d/40_custom
The downside is that the windows entry that works is below all the windows entries that don't. But the upside is that one of the windows entries works, so I'll live with it.