Batch Create give a success msg, but isn't successful

I'm trying to import about 200 sites/username, and I've followed the directions very carefully. Every time I run the import I see the progress bar, and then it stops and gives me a success message. But it isn't successful because it only imports one, sometimes two, sites and users.

I've quadruple checked the XLS sheet for correct/consistent/normalized data, and I'm doing it exactly as in the example. Should I try doing 10 or 20 at a time? I'd prefer not to, I have about 500 to create total.

Is there a setting that I'm missing, or code that needs to be written?