The following save in c3c v1.15b will not upgrade to v1.22.

Save v1.15b (http://www.civfanatics.net/uploads7/GGF3_900AD.SAV)

Can anyone offer advice as to why that would be the case?

I'm pretty sure that the 1.20 and later saves are not compatible with earlier games. I had thought they were....but I guess not.

You might want to try to patch to 1.20, load the game and save it as 1.20. Then patch to 1.22, and load and save. But I don't think this will work....:(