Anyone found out how to unlock Galaxy Mega bootloader or flash a custom ROM onto one?

[AC Question]

Ok, so my neighbour recently gave me an old Galaxy Mega (6.3). It's running 4.4.2 and, since Touch-Wiz is crap, id like to be able to flash TWRP and then a custom ROM. I have been using Odin but it always gives me;

<ID:0/004> Odin engine v(ID:3.1005)..
<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> recovery.img
<ID:0/004> NAND Write Start!!
<ID:0/004> FAIL! (Auth)
<ID:0/004>
<ID:0/004> Complete(Write) operation failed.
<OSM> All threads completed. (succeed 0 / failed 1)

I can't seem to get it to work. While the phone is in download mode, it says Write Protection: Enabled. I'm not an expert with Samsung devices but does that have anything to do with it failing? I read somewhere that you can disable some firewall (pretty sure doesn't exist) to disable the Write Protection. I do have the device rooted (somehow) and have even tried the TWRP Manager, buuuuut still nothing. After using the TWRP Manager now when i try to boot into recovery mode it says 'Non- ATT stuff blah blah detected blah blah" Any help would be greatly appreciated. Thanks

 

[the tall guy]

Hi, did you manage to find any more info out about this issue?