CSV file may fail to upload for 3 reasons:
1. It may contain special characters that is not recognized by the system.
2. It may contain blanks for some records which a standard csv file doesn't support.
3. The file may not have been encoded in UTF-8 format which is the most common convention for encoding csv.
If there are no issues in your file as mentioned above and still you are getting errors while uploading csv in Nurture, please send us an email with the attached file to support@nurturehq.com