In the most cases it's related to wrong CSV file structure. If you're editing file before import please make sure you keep it's structure untouched - otherwise our app will fail to read it properly.
In any case you may send your CSV file to our support team so we may check and let you know what exactly is wrong, and import it for you if needed (without any additional charges of course). You may send invitation to email@example.com. Please also send us an email to that address with your CSV file.