When I try to upload a contact list I get this error message "A field name was selected for more than one column in your file. To continue, please make sure that only one column is selected for each field name." After I called support we figured out that what you meant was that you wanted each *row* to have a unique field name.
Since you're unrolling a new file import procedure at the end of the week, this problem may go away. But you might plan to retain some of the features of the current procedure. If you do, it would probably help users if you checked to be sure that the error messages agreed with what users saw on their screens.