Also, although there is a ttk.py file in my python27\lib\lib-tk folder, there isn't a ttk.pyc file in there. I wonder if that's a symptom of the larger problem that's giving me the "cannot import ...

The problem I've noticed is that if I append the file with each of the 100k runs (one at a time), it can happen that two threads try to save to the file at the same time and some row (s) end up empty.