Item CSV Import > Error: Invalid vendor reference key xx

The error is caused when the Unique Identifier you are using in the Import is incorrect.  

Example:

1. Vendor name in the Excel file contains External ID values but in the Field Mapping page, you set the reference type to Internal ID.

1. Vendor name in the Excel file contains Internal ID values but in the Field Mapping page, you set the reference type to External ID
   
   To Resolve This:
2. It is recommended that you use the Internal ID of the vendor and include it in the Vendor column of your Excel file.