A Key Field is a required field for the import and is designated with an asterisk on the Import template. This issue is reported with this error message:
Cannot repeat key fields
Resolving the Import Error
If you receive this error, it means there is a duplicate Key Field. This often happens when there is a large document.
To resolve the error, check the error report for the line of the error. Look for the duplicate Key Field. This is most commonly the Name. Once you find the duplicate, you can either change the cell or delete the row if it is a true duplicate.