Thank you for bringing your concerns to the community! CSV files are one of the accepted formats for contact uploads, so you do not have to use Excel. Are you getting any kind of error message? If you can share what error messages you're getting, or let us know what happens when you try to upload that CSV file, we'll be happy to help get the issue you're running into corrected.
I am having with de problem, the file is a csv and I download of server, and later I upload on your server; but this show me on error:
Why happend is it?
I did upload this files without problems, and now this show the problem.
Thank you for replying back to us and providing a screenshot of the error message. I will like to look into this further for you. Could you please email us at social_support(at)constantcontact(dot)com with a reference to this post and the CSV file of contacts attached? Thank you.