That file from nexus is outdated, meaning it's still the old portrait file where all the portraits were together in a single huge file. With the update they divided the portraits into various more specific files. If you downloaded my file, you can edit it and it will work.
If you're using a software to edit it, instead of converting it, remember, when saving, to NOT generate MIP maps. Usualy the software give you this option when saving it.
EDIT: here, I edited it for you:
https://www.mediafire.com/?wdpg2rqaj1r7ecdPlease, all credit to the original mod and it's creator
http://www.nexusmods.com/divinityoriginalsin/mods/34/?If you download my modified file, please go download the original and rate it on Nexus.
I keep no credit for anything whatsoever and if anyone can contact the original creator, please let me know if he wants my file removed.
Thanks!