I decided to flash the stock firmware (ROM) back onto my Samsung Galaxy Note 3 as it was running some version that made it impossible to network unlock it.
I had to pay a few bob to download the ROM from “Rip Off” SamMobile.com, then went about installing it with Odin3.
But Odin3 frustratingly kept showing FAIL! with Hidden.img in the log section. (The FIX below).
One thing the instructions don’t say unless you read some or all of the comments is that there is no need to add the “.MD5” back onto the end of the file name once one has done the compression with 7.zip, doing so shows a MD5 error. Leave it as a .TAR file and it works perfectly.