Hi @user57746
I apologize you're unable to upload your contacts as easily as you should. Cases where users receive this error message we suggest adding headers to the file, or even sorting contacts so all email addresses are at the top of the spreadsheet. If you are still having this experience after trying these troubleshooting steps, please email us at social_support(at)constantcontact(dot)com a copy of this file. We would be happy to troubleshoot this further for you.