Could not boot Windows 8 from grub2 nor rEFInd on UEFI-system with Archlinux

I have followed the archlinux beginner's guide thoroughly and was able to install archlinux in UEFI mode and has been able to succesfully boot from it. Everything works fine except that I am unable to boot Windows 8 from GRUB.

I have tried os-prober,as suggested by the Arch Wiki; and when I boot from the menuentry generated by os-prober, it shows:

error: can't find command 'drivemap'.

error: invalid EFI file path.

Press any key to continue...

The following are the commands shown when i press e to edit the above menu entry:

setparams 'Windows 8 (loader) (on/dev/sda1)'

insmod part_gpt

insmod ntfs

set root='hd0,gpt1'

if [ x$feature_platform_search_hint =xy ]; then

search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt1 --hint-efi=hd0,gpt1 --hint-baremetal=ahci0,gpt1 5618A11A8A0F9DF

else

search --no-floppy --fs-uuid --set=root 5618A11A8A0F9DF

fi

drivemap -s (hd0) ${root}

chainloader +1

And I have also tried adding entries manually through /etc/grub.d/40_custom

menuentry "Microsoft Windows 8 x86_64 UEFI-GPT" {

insmod part_gpt
insmod fat
insmod search_fs_uuid
insmod chain
search --fs-uuid --no-floppy --set=root --hint-bios=hd0,gpt1 --hint-efi=hd0,gpt1 --hint-baremetal=ahci0,gpt1 5618A11A8A0F9DF
chainloader /efi/Microsoft/Boot/bootmgfw.efi

}

This is the result:

error: file '/efi/Microsoft/Boot/bootmgfw.efi' not found

Press any key to continue...

Please help!! I'd be glad to provide any additional Info needed!! Thanks in advance!! (do help me edit the formatting above, I'm quite confused by the usage of Blockquotes)