It might be that too many cards are being imported at once. The next version of the app won't have this restriction, but it looks like the current app crashes if you import between 100-150 cards (depending on exactly what's on the cards, and other factors that change from device to device).
Try splitting the cardset up into 50 card segments and importing them one at a time (in the application you can add them all to the same cardset).
Thanks,
Jason