After I applied your fix and loaded a game, the kelp files didn't load, but didn't stop the game from loading...
I initially had the same issue and it gave me a couple of error messages when loading the mod initially (before I had tried to load a save game) and it did stop my compatibility game save from loading, it froze at about 30% of the loading bar - but overwriting the revised kelp folder with the one from my original C2C v13 download did the trick (I guess I will have to wait for my next game to see the changes to kelp!!!)
So after swapping back the kelp folder for the one in the original C2C v13 download I was able to load my save game and found Jainism - so this fixed my game albeit with a few minutes fiddling about with the files (and that's not in any way a criticism, when I add mods to any game I expect a bit of fiddling about and wouldn't try to add stuff if I was reluctant to do that!)
Thanks again to Dancing Hoskuld for the fix