Note4 N910C (Exynos) can be rooted but my bootloader is locked. Howto unlock it?

Hi all,
I've been trying for over a week now to install a custom rom on my Samsung N910C (Exynos) OS=5.1.1 (Baseband=N910CXXU1C0J5).
I am able to root the phone and I'm able to install TWRP to flash a ROM. But I cannot install any bootloader as when I try via ODIN I get a fail with logs as follows:
-----------------------------------------
<ID:0/004> Added!!
<OSM> Enter CS for MD5..
<OSM> Check MD5.. Do not unplug the cable..
<OSM> Please wait..
<OSM> Checking MD5 finished Sucessfully..
<OSM> Leave CS..
<ID:0/004> Odin engine v(ID:3.1203)..
<ID:0/004> File analysis..
<ID:0/004> SetupConnection..
<ID:0/004> Initialzation..
<ID:0/004> Get PIT for mapping..
<ID:0/004> Firmware update start..
<ID:0/004> SingleDownload.
<ID:0/004> sboot.bin
<ID:0/004> FAIL!
<ID:0/004>
<ID:0/004> Complete(Write) operation failed.
<OSM> All threads completed. (succeed 0 / failed 1)

<ID:0/004> sboot.bin
<ID:0/004> NAND Write Start!!
<ID:0/004> FAIL!
<ID:0/004>
<ID:0/004> Complete(Write) operation failed.
<OSM> All threads completed. (succeed 0 / failed 1)
-----------------------------

I'd really like to install Dr Ketan's rom or Sweet_ROM_V17.1 but after flashing the ROM in twrp it goes into a bootloop. I suspect its because I need to install a bootloader.
Can someone offer a solution to my bootloader problem? I've tried a whole heap of bootloaders but it seems locked.

BUT when it does get into a bootloop I go back into ODIN and install the stock OS from sammobile (N910CXXU2COJ5_N910CGBL2COJ1_N910CXXU1COJ5_HOME.ta r.md5) and I get the phone back to factory stock.
I then can root it and install TWRP and try again.

Any help would be appreciated.
thanks
Sam
saru4

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