Hello @user203674 ,   I'd advise referring to our article on formatting contact files for import, to see if anything in that article applies to the files. Even if you didn't explicitly prompt any changes, the database in which you have them stored outside of your Constant Contact account, programs used to open the files, or any other number of technical things in the background might be causing the files to not be readable/compatible as they were previously.   If you're unable to figure out what the issue would be with the contact file, please call in so our phone support can securely collect the contact file for further investigation. If you're unable to call in, please reply to the automated @ mention email you receive from this response, with the contact file attached. ... View more