There are a couple of items to check before reporting this as a ticket:
- Do you have the column headings spelt correctly with NO capital letters?
- are there no spaces at the end of your fields (for example a space character at the end of an email address)
If these items appear to be correct, then please create the csv from scratch (ie create a new file) and try again, as the file may have become corrupted.
If the upload will still not work, please submit a ticket and attach the offending csv file.