As far as I know, those errors are never written to any log file. They're just tallied up as the load goes on, and you get to see a final number. I'm not positive, just pretty sure that's the case.
I've found a good way to figure out the errors is to simply look at your data in the database. if there are errors in loading the data, chances are good that some fields are screwed up. That'll give you a better indication of what went wrong.
