Hi I know it's been 4 months but I wondered if any progress had been made on this import problem?
I tried to export then import the same products.csv file using 1.2.1 but it failed with 'Data is empty or corrupted' message in FF38.0.1 but worked ok in IE11 and Chrome43.0.2357.81 m - all on win 7 64bit. I use Bitdefender av and disabling that made no difference in any of the browsers. Seems strange as it's usually IE that's out of step.
I'm just trying it out at the moment hence needing a quick way to import around 300 products from another cart.