The question appeared after asking this one. It seems that the Win8.1 UEFI x64 Boot Manager is unable to boot anything other than the windows itself (winload.efi). Trying to launch any other UEFI image (.efi) from it gives the error code 0xC000007B and I'm pretty sure that this isn't because of a missing file but instead because the file is 'invalid' as when I rename that file the error changes to 0xC000000F. I have disabled the secure boot but without any luck.
At the moment I'm trying to integrate the rEFInd bootloader. I can say that it's UEFI image is working as it is able to boot from a USB flash drive using the firmware. Using the Windows Boot Manager however give the same results explained above (error code 0xC000007B). At the moment my BCD configuration is (picture):
F:\rEfit\refind is the directory where refind is stored and "refind_x64.efi" is the program image.
NOTE: I'm also wondering are only UEFI images (.efi files) allowed to boot in an UEFI Windows and also what is the format of the non-UEFI one's (like
EDIT: Moving rEFInd to a standard directory ("EFI") didn't solved the problem.