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You need to go into the mod file (usually in your user's Documents/My Games/Sid Meier's Civilization 5\MODS/JFD's Civilizations - Brittany (Nominoe) (v 2)/Core) then open the file "BrittanyNominoe_GameDefines" with a text editor (noteblock, etc.)
Then look for the LEADERS section and the VALUES line. There should be a "ArtDefineTag" whose value is for the Burgundy mod for some reason. Change it to 'JFD_BrittanyNominoe_Scene.xml'.
Worked for you, should work for you.
No clue how you could fix this, so I'll leave this here.
Wonder why it would happen all of a sudden
I played another one of your civs before this (Laos) so not sure why this would be quite different (well, except for units, tech, etc.).
I tried about four times with the same results, i.e. CTD, so I think I'm going to move on for now.
Thanks.