That error is harmless, it's just the game gets confused with multiple choices of upgrade but it doesn't do anything.
Do you have a steam version of the game? If that's the case and you get a popup related to kingdoms.exe: "t's a common error with steam mods. To fix it you just need to copy medieval II total war exe file and rename the copy to kingdoms"
Also something to keep in mind when checking for errors in the log, in Configuration.cfg you need to change:
level = * error ## generates a smaller error log file. Use this setting during normal gameplay
#level = * trace ## Currently disabled. Generates a large error log file. Use this setting when tracking down a CTD
to
# level = * error ## generates a smaller error log file. Use this setting during normal gameplay
level = * trace ## Currently disabled. Generates a large error log file. Use this setting when tracking down a CTD
It can also be a corrupted download or a bad installation. Also try delete map.rwm in data/world/map/base