Database error when importing .csv

Hi
I'm a new user of this plugin, but I can't import csv correctly, it displays "Database error. If you were saving a newsletter try a table upgrade from the status panel."
There are no special characters in it... I tried importing them 10 by ten, etc... there's always this message.
I also tried to import 3 emails, ok, then for unknown reason, the 4th one causes the bug... and not always on the same email... it seems totally radom.

Any idea how to fix this ?
Best regards
Mitch