This is an old method, yeh I know. But not everyone moved on to the PowerShell yet.

Anyway, if you’re trying to import a CSV file to Active Directory, and got the error  message says:
Invalid file format. DN Attribute not defined

Just try to remove the Unicode switch “-u” from your command. If that works, then re-save (save as) the CSV file using Notepad, and make sure to select the unicode option, NOT the UTF-8

HTH some1